X-COM (Video Game)

The brainchild of Julian Gollop and other assorted Microprose personnel, UFO: Enemy Unknown was a strategy game produced in 1993 and unleashed upon the European gaming public. A year later, it jumped the pond to grace American players as X-COM: UFO Defense, since there was a naming rights conflict with an obscure 1989 flight sim by subLOGIC called UFO.

By either name, X-COM puts the player in command of an eXtraterrestrial COMbat unit charged with protecting Earth from an alien threat, managing resources and researching captured technology in the process. The hybrid of Real Time Strategy (improving X-COM's overall condition and catching UFOs as they land - or crashing them yourself) and Turn Based Tactics (exploring crash sites, stopping terror attacks, and defending and assaulting bases) quickly won the hearts of the gaming public.

More than 15 years after its initial release, UFO Defense still attracts players and tops lists of the Best PC Games of All Time. A 2007 assessment by IGN has it edging out fellow Prodigal Son of Microprose Sid Meier's Civilization IV for the Number 1 slot.

Not to say the X-COM legacy is a solo act, however. While Gollop's team set to work on X-COM: Apocalypse, an in-house crew at Microprose beat him to the punch with X-COM: Terror From The Deep in 1995, a Mission Pack Sequel created to satiate player demand for more alien-assaulting action. Apocalypse hit the shelves in 1997, to mixed reviews due to its Art Shift into pseudo-3D futuristic graphics and the clunkiness of a newly-introduced real-time option for playing missions. The last days of Microprose (and its acquisition by Hasbro Interactive) saw X-COM trying to get back on its feet with two Genre Shifted offerings: X-COM: Interceptor (1998) kept the base management elements while swapping out the strategy missions for space-bound Flight Simulator action, while X-COM: Enforcer (2001) ditched the strategy part outright to make a First Person Shooter running parallel to the timeline of UFO Defense. Sadly, neither had the mystique of their ancestors, and are often shunted away from canon due to the Unexpected Gameplay Change (and in the case of Enforcer, being awful).

While the X-COM license was passed through a variety of incapable hands throughout the 2000s, the earlier games attracted a variety of player-made mods and remake attempts in numerous stages of completion. Various Spiritual Successors also exist, such as UFO: Aftermath and its sequels Aftershock and Afterlight (unrelated to the game UFO listed above), the Game Boy Advance sleeper Rebelstar: Tactical Command, Laser Squad: Nemesis (in and of itself a sequel to X-COM's own predecessor Laser Squad) and UFO: Extraterrestrials which is almost an exact remake of the original game. All have attracted moderate attention from X-COM fans, largely for either the similarity in gameplay (the UFO Afterblank series) or the connections to Gollop and other former X-COM staff (Rebelstar and Laser Squad). Fans have also made their own remakes, most notably UFO Alien Invasion and Xenonauts.

Due to the entire series being re-released on Steam X-COM has experienced a resurgence among retro gamers, especially those eager to chronicle their campaigns.

An FPS reboot was announced in 2010, developed by 2k Marin, the team behind BioShock 2. The fanbase reacted in a manner predictable to everyone except, apparently, 2K Games, even going so far as to dub it things like "XenoShock" and "XINO" ("X-Com In Name Only"). This seems to be due to a combination of the bitter taste left behind by Enforcer and an understandable lack of enthusiasm for the direction the developers seem to be taking the game (with changes such as the possible wholesale dumping of the previous games' canon, X-COM being a division of the DoD as opposed to a Multinational Team, the focus era being shifted to a "Pleasantville" version of the sixties and the move from cerebral turn-based strategy to the Third Person Shooter gameplay seen in the trailer).

The fandom's response to the reboot announcement was heavy enough that Firaxis Games (a subsidiary of 2K) announced XCOM: Enemy Unknown, a new strategy entry in the series developed by Firaxis Games(Devs of Civ 5). And the Fandom Rejoiced! It was released with great anticipation on October 9, 2012. It was received well enough to receive an expansion pack, called XCOM: Enemy Within, which featured an expanded roster of human and alien units and technologies, as well as EXALT, a treasonous human faction. First-glance description: aping the "fancy" shooters with bells and whistles, Achievements, DLC, and graphics with pointless glowy bits, but game mechanics made in a solid style resembling Only War adapted for X-Com setting.

Meanwhile, the original reboot, The Bureau: XCOM Declassified, was released in 2013 to lukewarm reviews -- it wasn't bad, but it didn't wow anybody, either. After much speculation on the degree of canonical interconnection between the FPS and the strategy game, the case has been finally laid to rest by associate producer Pete Murray: "They're in their universe; we're in our universe," he says. "We do talk with [2K Marin], but thematically, they're separate."

In 2015, Firaxis announced a sequel to Enemy Unknown, simply titled XCOM 2, that's released on 5 February 2016. Rather than continue the storyline with the typical "Congratulations on defeating the aliens, now have some more aliens!" maneuver, XCOM 2 follows from a canon ending that XCOM lost hard. The aliens have taken over the planet, publicly appearing to be benevolent rulers. The remnants of XCOM went underground, suspecting that the aliens' motives were not so altruistic, and twenty years later, they're ready to bring together the various resistance cells and take back the planet.

General

 * Adventure-Friendly World: See Crapsack World - This works out fine as the backstory of a hyper-lethal squad combat game: the utter monstrosity of your enemy means that as long as any humans survive, the Non-Entity General can always find vengeance-crazed replacements for troops lost in combat, or at least someone willing to die for a carrot, and there is an unending supply of alien baddies to kill, capture and vivisect. But taken out of context, X-COM is essentially sending unaccountable death squads against an enemy that can never really be beaten without desperate measures.
 * Airborne Mook: The Floaters, their equivalents in the sequels and various terror monsters.
 * Alien Abduction
 * Alien Autopsy: The player's scientists can perform these.
 * Aliens Are Bastards: Played straight. Would have been subverted with the canceled Alliance, where the stranded X-COM team form an alliance with the friendly aliens against the hostile ones.
 * Partially averted in Apocalypse. The new aliens are certainly bastards, but some of the ones we've been previously familiar with no co-exist peacefully with humans.
 * Alien Blood: Green and Yellow seems to be most common ones.
 * Ethereals have silver blood (though it's dark red in its Autopsy picture), Aquatoid blood is orange, and Lobsterman blood is teal.
 * Alien Invasion: Duh.
 * Aliens and Monsters: Mostly aliens, but their Terror Units are often engineered (genetically or otherwise) to either capitalize on their owner's strengths (Chryssalids having weaponized the Snakemen's rapid asexual reproduction, for example) or cover their weaknesses (Sectopods distracting the enemy with conventional attacks while their Ethereal masters make with the Mind Rape). Except for the Silacoids and Celatids, which (given that their counterparts the Mutons don't really have weaknesses) don't really do anything.
 * Aliens Steal Cattle: Several missions involve "Harvester" UFOs sent to meet the aliens' carnivorous needs. They are, of course, equipped with Cow Tools.
 * All Your Base Are Belong to Us: A major gameplay element; you have to design your hidden underground bases with defense in mind, since aliens will eventually find and attack them. Later in the game, of course, you get to do the same to them. (Or earlier, since unless you're doing a really bad job, you'll find some alien bases before they find yours.)
 * Alliance Meter: UFO and TFTD has this in form of Funding Nations. Scaled up in Apocalypse with 25 factions waging corporate wars for political and economical power in Mega-Primus during the alien invasion.
 * Almighty Janitor: Your newly hired and unranked recruits, thanks to their randomly created stats, are potentially capable of being incredible marksmen, Made of Iron or - when you have researched a Psionic Laboratory - mindraping any alien they see into commiting treasonous and suicidal acts of violence against their own side. (But more likely they're completely useless and you'll have to sack 8 out of 10 when you finally get their psi evaluations.)
 * If you know what the limits are for a fresh recruits stats (for example, they can start with 40 to 70 time units), then you'll quickly realize that most of your recruits literally are cannon fodder, being at the bottom rung of effectiveness.
 * Alternate Continuity/Continuity Reboot: XCOM: Enemy Unknown/Enemy Within serves as this to the original games, with XCOM 2 following up from that. The Bureau meanwhile serves as an alternate prequel to both the originals and XCOM: EU/EW, though it exists in its own continuity.
 * Anyone Can Die: And anyone WILL die until you've got solid armor research going. Or even afterward (see Armor Is Useless).
 * Apocalypse How: The result of failing to defeat the aliens (and sometimes even when succeeding). See the more detailed AP examples in each games respective sections.
 * Appropriated Title: The series started as UFO: Enemy Unknown. It had to relabel itself X-COM when somebody complained there's already a game called UFO.
 * Armor Is Useless: X-COM soldiers, as units without resistances, take 0 to 200% of the listed damage from firearms; 50 to 150% from explosives. A soldier with maximum health and the best armour can still be killed in one shot if the damage roll is high enough.
 * Unarmoured troopers can survive several heavy plasma blasts and take absolutely no damage... only to be offed by a single pistol shot the next turn.
 * On the other hand, the better armors available for X-Com Agents render at least normal weak weapons useless against them. Of course, the only benefit of being immune to rifle bullets is that if your friend carrying a normal rifle gets mind-controlled, he can't even dent you by shooting you in the back.
 * In addition, the Power Suit also makes it possible for agents to use Autocannons loaded with explosive ammunition in close-quarters combat with little risk of being badly injured by the splash damage.
 * Truly badass and lucky troopers can claim to survive point-blank Blaster Bomb detonations thanks to this.
 * However, any way you slice it you can never actually count on armour, since all gun-toting aliens use plasma weaponry and most use Heavy Plasma, unquestionably the most powerful (non-explosive) personal weapon available. Even a Power Suit only gives your soldiers about 50/50 odds of surviving even a single shot.
 * One selling point of the various armors in the original, they protect your soldiers from damage if standing in fire. Later sets also prevent "stun" from building up while standing in smoke.
 * Mostly averted in TFTD, the front of the Ion Armor can let soldiers take point blank Sonic Cannon blasts or Lobstermen's claws and take no damage as long as it hits the front armor (unless random chance screws you over). But still played straight with Bio Drone explosions and Tentaculats.
 * Averted in Apocalypse. Megapol Armour is fairly competent, particularly against light friendly fire and early disruptor weapons, but is terrible against devastators. Marsec's flying armour is weaker but allows flight. On the other hand, X-COM manufactured "Disruptor Armour" transforms soldiers into nigh-unstoppable death machines who can practically waltz through multiple explosions without even taking a mortal injury. The shields certainly help, though.
 * Artificial Stupidity: The civilians in Terror Sites. They will run through a door, back through it, then back AGAIN. That is if they are not running into the middle of fire fights, because the natural place to stand in a military operation is DIRECTLY IN FRONT of the man with the laser rifle.
 * A-Team Firing: Most recruits will hit [[media:AW-XCOMAccuracy.jpg|everything except the aliens]].
 * This is especially evident when using Auto Fire (which makes soldiers shoot 3 less-accurate shots in rapid succesion). Agents can even be firing an accurate weapon like any of the Rifles at point-blank on full auto and have the shots knock down the walls and trees behind an alien without even grazing it. On the other hand, Aimed Shot (a single more-accurate shot that uses up more of your Time Units for the turn) is actually very effective with enough training in Firing Accuracy.
 * Auto shot is preferable early on when you know even the soldier's aimed shot will most likely miss. First, it have a chance to hit aliens multiple times, stray bullets will sometimes hit other aliens even those you didn't notice, and if the alien can see you, a single burst will only trigger one reaction fire as opposed to aimed shot or snap shot which triggers reaction on every shot. Once you have laser weapons, you most likely use auto shot at every opportunity.
 * Experimentation has shown a few oddities with accuracy in the first two games. In particular, the quoted % accuracy is actually understated a majority of the time. The reason for this is that a "miss" is not actually a miss, but rather a random deviation applied to the bullet. If you're lucky (or at point blank range), this deviation will be small enough that the bullet hits anyway.
 * Attack Drone: Cyberdiscs and Bio-Drones.
 * Enforcer's protagonist. Recursively, he too can get an Attack Drone.
 * Authority Equals Asskicking: Aliens only in the first two games.
 * Not necessarily true with human soldiers, depending on whether the player has the officers on the battlefield getting exercise along with the other soldiers or leaves their muscles to atrophy in the back of the Skyranger.
 * Awesome but Impractical: Several weapons and base components, either due to how easily their replacements can be researched or by being Nerfed by the game mechanics.
 * The Sonic Cannon of TFTD is the biggest offender. It can firing snap shots or aimed shots and inflicts about 15% more damage than the Sonic Blasta-Rifle. However, firing a snap shot will take half of your time units, and an aimed shot requires 75%, meaning you have almost no ability to manuever. In addition, due to the weight it's less accurate the Blasta-Rifle, and has five fewer rounds per clip, and is so heavy you're limited in what else you can carry. The Blasta-Rifle is superior in every way except damage, but since you can fire two snap shots and move with the Rifle, the slight damage increase the Cannon offers is negligible. Fortunately, the computer will use the Cannon, and all it's attendant problems, exclusively about two-thirds of the way into the game.
 * The Griffon Tank in Apocalypse: Huge, has a BFG. Awesome stats for something you can get at the start... but because of a coding decision, will be destroyed if the road under it gets damaged, no matter what its current health is.
 * Rocket/Torpedo/Missile launchers. While precise and powerful, one aimed shot in two turns or one snapshot and reload each turn doesn't look so great when you have a weapon with explosive damage and decent rate of fire - and grenades.
 * E.g. in the first game: 115% Accuracy is nice, but usually you fire those at big targets, and given the blast radius, if you need this accuracy, you are desperately gambling, or something else has gone wrong already. HE Missiles have damage 75 (Small, $480/1) or 100 (Large, $720/1). One small missile weighs like a magazine of 6 Heavy Cannon HE shells and costs twice as much. Those do 52 damage each - most of the time still enough to one-shoot a Reaper on medium difficulties; you don't need to reload after every shot and get up to 3 snap shots per turn. Heavy Cannon is more expensive, but 3-4 missiles will eat the difference. Much the same applies to Auto-Cannon, only more expensive, less accurate, and with 44 damage only the wimpy enemies fold from one near hit... but you can fire in bursts and pack lots of these rounds. Now, a hand grenade does 50 HE damage, weighs half as much as Heavy Cannon magazine and costs somewhat less - everyone whose main weapon is not Heavy Cannon or Auto Cannon can carry at least one... oh, and at the start most likely half of your soldiers barely can hit a barn with auto-fire, but are hitball gods.
 * Awesome Personnel Carrier / Cool Plane: The Skyranger VTOL jet.
 * Terror from the Deep introduces the Triton, a submarine equivalent of the Skyranger.
 * The ultimate troop transports (the Avenger, Leviathan, and Annihilator) are also the ultimate fighter craft!
 * Badass Normal: Any human who lives long enough. Everybody starts out as a Red Shirt, but over time they can become absolutely terrifying, some even capable of single-handedly slaughtering entire alien craft full of enemies in a single mission.
 * I have several instances of a single soldier in TFTD with ion armor slaughtered everything in a medium USO with just a Thermic Lance.
 * Bee People: The Sectoids and Aquatoids are described as such. The Apocalypse aliens as well.
 * BFG: The series is full of them, from the Heavy Cannon to the Rocket Launcher to the Heavy Plasma to the Blaster Launchers and their counterparts.
 * Bizarre Alien Biology: Autopsy results - Some are fairly mundane, some are heavily cybernized, and some who by all means should have been dead when they were alive.
 * Black Box: Even when research is done, there are still something that bugs the scientists, usually the autopsies of the more exotic aliens and miscellaneous tech. They sensibly ignore it rather than taking the (extra) time to figure it out.
 * Body Horror: Chryssalids, Bio-Drones, Tentaculats, several of the Apocalypse aliens, and so forth.
 * Bottomless Magazines: Only for laser weapons in the first game, the major reason they are so good. Hideously averted for everything else (see Easy Logistics below) except for aircraft and HWP energy weapons and even those just have very large magazines (100 or 255).
 * While the first game went with the "more powerful weapon = more ammo in clip" method (the plasma pistol has 15 rounds, while the heavy plasma has 35), TFTD decided that more powerful weapons need smaller clips (the Sonic Pistol has 20 rounds, the Sonic Cannon has 10).
 * Brainwashed: The common state of victims of Ethereals, high-ranking Sectoids, and their successors. Often, they're also crazy.
 * Bullethole Door: Great for reducing the effects of Dronejam during Terror Missions. Busting through the walls of UFOs, however, will take well-placed/lucky plasma holes (interior) or Blaster Launcher shots (exterior).
 * Or lots of plastic explosives, but that's another trope entirely.
 * Charles Atlas Superpower: With sufficient combat experience, a soldier can eventually beat out a tank in health, movement, accuracy, etc. Oh, and tanks can't get those nifty Psi abilities. Though are immune to mind control themselves.
 * XCOMUtil's modified HWPs, on the other hand, are absolutely terrifying, and are capable of reliably hitting an enemy from a considerable distance away. And if they miss, well, that's why you use the Rocket Tanks... until you get the Fusion Ball Tanks. Which can never miss, unless you're bad at setting in the missile course.
 * Also demonstrated by Commander units on the enemy forces, particularly in X-COM and TFTD. Your average Floater, for example, dies if you so much as glare at it. Floater Commanders can take several rifle rounds to bring down, on the other hand. Rank distinctions were removed in Apocalypse, however, though enemy stats could vary greatly.
 * Chest Burster: Chryssalids and Tentaculats.
 * The Computer Is a Cheating Bastard: Most prevalent in UFO Defense, where aliens don't suffer from Fatal Wounds unless they were inflicted under previous mind control, magically know the entire map (and your soldiers' positions) after Turn 20, and can target any of your soldiers as soon as just one is in visual range (particularly rage-inducing with Ethereals' psi-spamming).
 * Even so, it's possible to fool them by bringing a psi-decoy with low mental defences and no weapons (if you want to keep one somewhat useful with zero damage capability, there are medi-kit, mind probe, smoke grenades and flares) to suck up all their psychic powers, as they are always going to target the people with the weakest minds.
 * Thus making that poor bastard a Mind Rape Unwitting Pawn.
 * The aliens were also capable (in TFTD, and presumably UFO Defense) of hiding in squares that were in line-of-sight. Finding a lobster man three squares away with a blaster launcher just outside the final room of T'leth is an unpleasant surprise. When the discovery takes place because it rotated where you could see it after you'd specifically looked in that corner...
 * Colonel Badass: The Commanders of both sides.
 * Combat Medic: Anyone with the medkit, and boy, you're gonna need them.
 * EVERYONE should have a medkit. No exceptions.
 * You can also pick up a downed soldier's own medkit and use it on him, as knocked-out soldiers will instantly drop all their equipment on the ground.
 * Cool Starship: Completing a game often requires research and construction of an "Ultimate Craft" and interrogation for the whereabouts of an alien stronghold to drive it to.
 * Cow Tools: Aliens bases and some ships are filled with these. Some you can research, some just look appropriate.
 * Crapsack World: An unknown, but likely large portion of the galaxy is ruled by a Completely Monstrous Hive Mind - Sectoids and others are obviously treated as expendable. Humans might be able to destroy the local node if they become The Unfettered - abolish every civil liberty and article of war. And there's another, unattached(albeit slightly less advanced) node in the Gulf of Mexico. And its destruction would reduce Earth's biosphere to the algae level. And there's an entire planet of Hive Mind aliens just one dimension over. And the best weapon against all these irredeemably hostile aliens are Half Human Hybrids with Psychic Powers... who will eventually become a permanent underclass treated like parolees from cradle to grave and not allowed to breed without permission(which tends to be withheld between invasions).
 * Critical Encumbrance Failure: Of the "carry items up to the soldier's Strength in weight, then take Time Unit penalties for going overboard" type.
 * Critical Existence Failure: Averted - Soldiers lucky enough to survive alien gunfire (and that won't be many of the unarmored ones, mind you) will leak HP from "Fatal Wounds" to their various body parts until they fall unconscious and are either treated with a Medi-Kit or left to die. More often than not, it's the latter. Wounded troopers also suffer an accuracy penalty. Unconscious soldiers (like corpses) can be utterly destroyed by modest explosive damage, however.
 * Played straight with Cyberdisks. Due to how 2x2 monsters work, a stunned cyberdisk is effectively a dead cyberdisk. Actually killing it results in a rather impressive boom. Which can also cause chain reactions, if other cyberdisks are close enough.
 * Played straight in Terror From the Deep with Bio-Drones.
 * Crouch and Prone: In UFO and TFTD Soldiers can crouch to improve accuracy, become a smaller target, have more cover and to allow the standing soldiers behind the crouching ones to shoot over their shoulders (though be careful, there's still a risk of hitting the guy in front of you). Soldiers automatically stand up straight when moving. Apocalypse also has a prone position.
 * Death From Above: The Floaters and their equivalents. Players can also do this once they research a means of flying.
 * Some Enforcer enemies will do this. In particular one floating buzz-saw thing likes to reach you and flip up to where you can't possibly get an angle on it, attacking all the while.
 * Decapitated Army: In most games killing the alien leader and destroying the main base he was in makes you a winner.
 * Deconstruction: Of children's cartoon series such as G.I. Joe and Transformers. X-COM is a team of elite soldiers who wear cool-looking armor and have a fancy Cool Ship that they travel the world in to save the world from goofy-looking aliens...and then suffer a relentlessly high fatality rate, crippling technological inferiority, and severe funding troubles. Anyone Can Die, often in rather brutal ways, and 50% or higher casualty rates are common in successful missions, with failures usually resulting in no survivors whatsoever. The cool-looking armor is good for little else besides appearance. The Cool Ship costs ludicrous amount of money to lease and is completely unarmed. The goofy-looking aliens outnumber us over a thousand to one and have technology that outstrips ours to such a degree that X-COM might as well be fighting them with sticks. The Man in Washington will happily cut funding at the drop of a hat, even if there's a UFO landing outside the White House. It is not a very pleasant situation. Ironically, after Hasbro acquired the franchise they briefly attempted to make it into a children's cartoon series, which is a rather curious decision considering X-Com's almost insanely high casualty rate.
 * Destroyable Items: If it's in someone's hands, it can withstand a nuke, but once it's dropped on the floor, it will be removed from existence by a firecracker. Explosions can destroy any object lying on the ground, including corpses, unconscious units, and loot. That said, some items are tougher than others: Electroflare is destroyed at 8 damage, Plasma Rifle or Heavy Plasma at 50, i.e. a conventional grenade destroy them only if it explodes at the same map tile.
 * Repeat after me: no grenades or rockets in the alien engine room - the power source itself is fairly tough, but Elerium is an item on the floor (you can see it on mini-map) and like the rest of them, evaporates if subjected to a strong sneeze. Oddly enough, ammunition and other explosives can be either unaffected by explosions or utterly obliterated in the first games. Horribly not so in Apocalypse.
 * Disadvantageous Disintegration: Someone got hit with the Blaster Bomb to the face in the room full of stuff Made of Explodium? No trace of a body and equipment.
 * Disaster Dominoes: What happens when your units are low on morale.
 * Doing Research
 * Dronejam: Civilians are NOT your friends during Terror Missions. They move about at random, block your movement from place to place in the process, provide excellent breeding opportunities for Chryssalids outside of your visual range, and turn hostile when you mind-control them away from enemy fire (thankfully, as they're unarmed, it's a token hostility). If you're not particularly concerned with their well-being, then what's another few human casualties alongside your squaddies?. Otherwise, check the page for nonlethal civilian control methods of varying degrees of effectiveness and hilarity. If the given version allows to use Stun Rod on them, it's the way to go for those strong enough to carry it - nothing bu fire and explosions harms an unconscious unit.
 * Drop Ship: Skyranger and Triton from UFO and TFTD respectively.
 * Dude, Where's My Respect?: You're up against the outer space equivalent of the Legions of Hell, including little gray men that indulge in abduction and cattle mutilation, roaring space orcs that can survive a direct hit from missile launcher and killer crabs that give a Face Full of Alien Wingwong. The Funding Nations don't really care about your situation, and sometimes consider siding with Aliens as a better alternative.
 * Dummied Out: One of the many things left unused is the "Alien Reproduction" item and research line in UFO Defense - strange considering the resultant Half Human Hybrids wind up playing a key part in Apocalypse. The sequels also include other things that were ultimately left out due to time and budget constraints.
 * Apocalypse also contains Procreation Parks, buildings in Megaprimus where couples go to have their children grown in artificial wombs, matching the dummied out research text of the above: "The process could be easily adapted for human reproduction".
 * Dungeon Bypass: Tired of slogging through Cyberdisks and Sectoids while being panicked and mind-controlled? Breach the hull at the top floor and reach their Leader immediately with a Blaster Bomb! Other weapons can also breach the less-durable inner walls of UFOs, and human buildings are all too easy to destroy. A common early-game tactic is to spam rockets and autocannon grenades on buildings that aliens might be hiding in rather than engage in costly room-to-room or building-to-building combat.
 * In Apocalypse, collateral destruction is a viable strategy, if you didn't mind getting stuck with the bill. Instead of scattering troops across large, multilevel facilities to hunt down aliens in dark corners, you could set fire to or blow the floors out from under their suspected hiding places and wait for the sound of their screams. Or just level the building with your combat vehicles.
 * Dynamic Difficulty: Regardless of the difficulty your campaign starts at, most of the games will see fit to ramp up alien activity to correspond with consistent positive performance.
 * A bug in UFO Defense caused the difficulty to reset to beginner no matter what you actually set it at. Because of this, gamers complained that the game was (relativly) easy, which made the developers of TFTD increase the difficulty across the board. The result was a ridiculously hard game.
 * If you don't eventually go for the Big Bad in TFTD, alien bases will start to proliferate faster than you can keep up with them.
 * This is the whole point: you are fighting a losing war against superior technology. If you do not exploit their weak point by finding the Big Bad, the enemy will become stronger and stronger until you have no chance of survival. This is done on purpose.
 * Earthshattering Kaboom: Interceptor's Nova Bomb is designed to take out a star and everything orbiting it (a lower-level Class X-2 on the Apocalypse How scale).
 * Blaster Bombs could certainly count, as well as Cyberdiscs, particularly when chain reactions are caused. But as we already know, they're Made of Explodium.
 * Repeated explosions will start to dig a hole in the ground. In UFO Defense this hole is purely a visual artifact as eventually concrete or a road will be destroyed exposing dirt...at the same level. In TFTD, most things take place on ground anyways but it still happens in port terror missions. In Apocalypse, as the Let's Play demonstrates, it's possible to accidentally end up digging an enemy that can withstand multiple missile hits a foxhole.
 * Easy Logistics: Averted so very hard. While ammunition for conventional weapons can be bought as long as you have money, more advanced weapons require manufactured or captured ammunition to work. And then there's allocating a limited stockpile of Elerium between manufacturing and aircraft fuel.
 * Moreso when XComUtil's "Improved Laser Weapons" fix is implemented. Sure, the Heavy Laser finally gets Auto Shot capability, but must it come at the cost of using Elerium for Laser construction AND not being able to make Plasma weapons (even after taking into consideration that the aliens drop Heavy Plasmas like candy)?
 * Elaborate Underground Base: A necessity due to X-COM's covert nature, often leading to All Your Base Are Belong to Us should the aliens stumble upon it (hopefully "them" by the time an Alien Retaliation fleet comes calling).
 * Aliens get these, too. Which you have to break into to kidnap high-ranking officers for interrogation to complete the game.
 * Enforcer does this in a few levels.
 * Elite Mooks: Alien Squad Leaders in general. Later-Game Aliens (Mutons, Tasoth, Lobstermen) also may count.
 * Enforcer bosses, which are usually giant versions of other mooks like Reapers or Chryssalids, with special attacks.
 * Emotion Bomb: "Panic Unit", the easier use of psi powers.
 * Enemy Detecting Radar: Motion Trackers, though they can only detect units that moved within the last turn. So always check the corners in case something's lurking.
 * Enemy Scan: Mind probes.
 * The Enemy Weapons Are Better: Damage wise at least.
 * Energy Weapon: Laser and Plasma weapons.
 * Encyclopedia Exposita: The UFOpaedia in its various forms across the generations. Even more so the fansite of the same name.
 * And this is more or less an online version of the in-game UFOpadias.
 * Everything Breaks: At least, it gives you an option to deal with the Insurmountable Waist-Height Fences. But not everything breaks easily. In the unmodified original X-Com, the only way to breach the hull walls of UFO is Blaster Bomb. And normally, solid walls are set to weaken the propagating explosions by the same damage it takes to destroy them... however, many maps are made buggy in a way that allows even lesser explosions to pass right through some walls without weakening. An interesting side is that explosives cause flat 50% of their stated damage, decreasing with range from ground zero (the pattern of destruction from the same munition at the same place on the map is always the same), while other weapons do 25%-75% of the stated damage. A modest Laser Pistol (base damage 46) may destroy any wall Heavy Cannon HE round (damage 52) would, and some things it couldn't... but will it this time?
 * In fact, one valid strategy in the first games is to remember that on most missions civilians are absent and remove the scenery with explosives or lasers if it can be an ambush site, like those barns.
 * Exclusive Enemy Equipment: The few thing that your technicians cannot reproduce.
 * Executive Meddling: Showing that Tropes Are Not Bad, the original X-Com actually owes many of the things that make it famous to Executive Meddling. Initially, the game was going to be a pure tactical combat game set in an alien world; executives demanded the addition of the larger strategical game to tie things together and asked that it be set on the more familiar setting of Earth instead.
 * Exploding Barrels: Fuel drums and warheads of missile defences in your bases, gas pumps in Terror Missions, and certain UFO components all explode when shot. Frustratingly, items caught in explosions are usually destroyed.
 * In TFTD, the normal skirmishes (USO Recovery) sometimes have what seems to be oil pumps. Also, apparently sunken aircraft's engines are Made of Explodium.
 * Face Full of Alien Wingwong:
 * Chryssalids, oh God, the Chryssalids... Tentaculats and Brainsuckers fill their niche in Terror From The Deep and Apocalypse, respectively.
 * Brainsuckers represent an absolutely straight case of Face Full of Alien Wingwong, no less, attaching onto your head and emptying their innards down your throat. And cross it with People Puppets. On the downside, they hatch from pods shot from special launchers, thus may pop up anywhere. On the upside, unlike their earlier brethren, Brainsuckers are not only flimsy, but die when trying to take over the victim, so if you make sure the closest soldier is an immune Android, any brainsucker not shot en route will kill itself trying to infect steel.
 * Fake Difficulty: TFTD was probably the worst offender, but the game balance would not suffer if the standard rifle from UFO Defence were capable of reliably hitting anything a distance greater than it could be thrown. Lampshaded regularly in the Let's Play.
 * Fan Remake / Fan Sequel: Free ones include (and are not limited to):
 * UFO2000
 * UFO: Alien Invasion
 * OpenXcom - FLOSS engine using original data from the first two games. Has a lot of improvements, mostly optional (preserving the original behaviour if you want) and toggled one by one:
 * Fixes, including those from XComUtils and UFO Extender (polynominal accuracy calculation for "soft" effective maximum range, enable Pistol-Whipping, etc). E.g.: promote only soldiers who actually participated in a mission, enforce storage space not only for purchase, start psionic training at any time of the month.
 * Gameplay options - allows to plan your first base, better vertical propagation of area damage, extra movement modes (soldiers can run and strafe, tank can turn only the turret) gameplay elements from XCom 2012 (researched items are destroyed, weapons self-destruct if the alien is killed) and TFTD rules for items manufacture and weapon damage (all 50-150% rather than 0-200% for all but explosives).
 * "Modernized" features: key binding, AI improvements, graphics improvements (you can choose scaling level and method, also better globe lighting), visual elements (e.g. displaying TUs for path before walking and adjusted accuracy).
 * Depending on the version, ranges from mod-friendly (1.0 release) to very mod-friendly ("Nightly" betas) - which among the other things allows more fixes (like "Aliens Pick Up Weapons" mod fixing the old design oversight).
 * UFO: The Two Sides
 * Commercial ones include and are not limited to the UFO Afterblank series, the UFO: Extraterrestrials series, and Xenonauts.
 * Flaming Skulls: Skull-shaped explosions.
 * Friendly Fireproof: Averted, and with the average accuracy of X-COM soldiers, frequently painful.
 * Frickin' Laser Beams: The Laser weapons obviously. In the first X-COM, they're extremely useful throughout the early and mid-game and retain effectiveness in the late game, as they use no ammunition. Laser pistols also have the added advantage of an very low TU cost to their autofire, making them ideal for room-to-room combat against anything short of Mutons and Snakemen missions with Chryssalids. Sectopods, the Ethereal's terror units, are more vulnerable to laser beams than plasma.
 * Gatling Good: The Autocannons and their successors. Regular and incendiary ammo rapidly become obsolete (except for terrain cleaning and that one incendiary bug), but high explosive rounds remain viable throughout the game. Being able to saturate an area with high-explosive bullets never ceases being effective or awesome.
 * Genre Savvy: You're going to need to be in order to win. Just remember; if you they don't make the death scream, they aren't dead.
 * Genre Shift: What happened to every single X-Com game after the third one.
 * Geo Effects: On the Strategic scale, where you land determines what kind of terrain it will be in the battlefield. For example in TFTD landing in seas around Europe makes it very likely that the mission will take place among the Underwater Ruins, and in the very deep areas it's dark as in the night mission even during the day.
 * Giant Mook: Many terrorist aliens. The Megaspawn from Apocalypse. Enforcer bosses.
 * UFO Defense gives us the Reapers and Sectopods, the former a glorified alien attack dog and the latter a heavy assault mecha. Terror From the Deep has the Xarquid, a giant nautilus, the Triscene, a dinosaur with Sonic Cannons, and the Hallucinoid, a prehistoric jellyfish with chemical freezing agents.
 * Giant Enemy Crab: The Chryssalids in UFO Defense and the Lobstermen in Terror From the Deep.
 * Global Currency: Everything bought and sold in the main games is apparently done so in U.S. dollars.
 * Glorious Mother Russia: And they're surprisingly badass, too - Russia is the only nation in the game that can never be subjugated by the aliens, no matter how bad things get. They'll fight until the last man falls.
 * Grenade Hot Potato: With a little coordination and luck, a soldier in the back can prime and pass a grenade to the front.
 * The Greys: But of course.
 * Grid Inventory: Multiple grids throughout the body and uniform (and multiple Time Unit costs for movement of items from location to location) make a refreshing take on the Inventory Management Puzzle.
 * Arbitrary Equipment Restriction: The true Inventory Management Puzzle (at least in the first games) was deciding what 80 pieces of gear to bring along on a mission. It's more than enough for ten soldiers on a Skyranger - they can't carry this much without slowing down anyway. A fully loaded Avenger/Leviathan (holding 26 soldiers) could consume 52 of those slots just giving each soldier a gun and its ammunition. And that's without bringing extra ammo for reloading.
 * This is why you use lasers. Really. Saves ammo slot and you don't need to bring plasmas... :-)
 * Guns Akimbo: Not a good idea with two-handed weapons, obviously - accuracy drops. With pistols, it can be done, but pointless. Doing this in UFO and TFTD gave you another weapon to fire from, but TU are spent from the same pool, so the sum total of possible shots does not change. In real-time mode of Apocalypse this can help, as each gun counts rate of fire separately... but if you want More Dakka, it's easier to use a proper rapid-firing weapon than two pistols.
 * Hive Mind: The aliens in UFO Defense take orders from one, another in Terror From The Deep tries to play Cosmic Horror while it's at it, and the Biomass in the UFO games is a weapon designed to turn a planet into one.
 * The true threat in X-Com Apocalypse are actually colonies of microscopic organisms that are sentient in groups. Every alien life form you encounter in that game is merely one they've managed to take control of and manipulate to their own ends; the "brainsucker" life form that turns your comrades against you just injects their brains with an overload of micronoids. Late in the game, some UFOs try to take control of buildings and organizations by directly sprinkling lots of micronoids onto the building in question to influence the minds of those within.
 * Hold the Line: The objective of any Base Defense mission. Can literally turn into Hold The Line if you choose to adopt such tactics, although in some cases it's not so much line-holding as shooting fish in a barrel with a BFG.
 * This probably only applies if your base is attacked early in the game where aliens' psi attacks turn it into a nightmare. But, once you screened your recruits (and sack or reserved for medic duty the weak minded ones) and researched alien weapons, even if you have poorly designed base, a defense mission is just a shooting gallery.
 * Of note, the first base you build is horrifically designed. Four scattered access points means that any alien attack will inevitably result in long hours of slogging through narrow corridors, hoping the last alien doesn't get the drop on you (which it will). Even worse, due to the cost of research, manufacturing and hanger facilities, it will be your central headquarters for most of the early-to-mid game. Unless you're willing to invest months of game-time and millions of dollars rebuilding the base, your best hope is that it won't be found. And if you're doing particularly well in the region that your base is established in, it will be found.
 * One early Enforcer mission. It will make you want to scream and cry at the same time.
 * Hollywood Healing: Averted, wounded soldiers have to stay on lengthy medical leaves, with the most serious cases taking months.
 * Hover Tank: With your choice of Fusion Bomb launcher or Plasma cannon. Arguably, the Cyberdisc can be considered one of these sans turret.
 * Humanoid Aliens
 * Idiosyncratic Difficulty Levels: Beginner, Experienced, Veteran, Genius, Superhuman. Apocalypse is a bit simpler: Novice, Easy, Medium, Hard, Superhuman.
 * Harder Than Hard: Superhuman.
 * Easier Than Easy: Beginner/Novice.
 * Immune to Bullets: Because of how armour works and damage is rolled, certain enemies are actually immune to standard rifle or pistol rounds. Some are even highly resistant to otherwise powerful alien weapons (hello, Sectopods and Lobstermen).
 * Imperial Stormtrooper Marksmanship Academy: Best way to describe the accuracy of any Rookie. They can literally open a door, find themselves toe-to-toe with an alien, fire repeatedly at it, and still miss. Bonus points if their Shooting Accuracy is low. More bonus points if attempting to Auto Fire. Jackpot if they're suffering from Fatal Wounds in one or both arms. (The aliens' snap shots tend to be considerably more accurate ...)
 * Ocasionally subverted by the odd rookie trooper who has uncannily high accuracy and can out-shoot some of your crack troopers.
 * Can be double-subverted as well, as when a rookie used autoshot with laser rifle and failed to hit the sectoid he was aiming at, instead hit a cyberdisk behind it which blows up and kill several other aliens (and an unfortunate civilian) near it.
 * Imported Alien Phlebotinum: About 75-90% of gameplay revolves around the acquisition, understanding, and implementation of cool alien toys. Or in the RPG terms: Kill them, take their stuff, reverse-egnineer it, Repeat.
 * Reversed in Apocalypse: when you sell some of your stuff to a Mega Corp that's been infiltrated by aliens, the aliens will import your phlebotinum.
 * Though even if you keep infiltration at a flat zero through agressive building searches, the Anthropods always seem to get their misshapen hands on some Megapol smoke grenades - the buggers know how to use them to clear stun-gas clouds, too.
 * Instant 180 Degree Turn: Averted. Turning costs Time Units, though it will not trigger alien reaction fire. Sometimes, troopers who have to turn to face the enemy wind up without sufficient TUs to take the shot.
 * Item Crafting: Sort of. Manufacturing most things includes component items in addition to non-specific expenses and work time.
 * It's Up to You: Since all of the world governments have tried and failed to handle the aliens, it's up to X-Com to get things done. Although it wouldn't hurt if the local governments lent a hand during Terror Missions.
 * Played even straighter in Terror From the Deep. X-Com was disbanded after the end of First Alien War, and the world governments don't have the advanced technologies they developed to confront the new alien threat. Once again, it all comes down to X-Com.
 * Kill It with Fire: There's always incendiary.
 * Law Enforcement, Inc.: After the Second Alien War of TFTD X-COM becomes this to avoid underfunding. X-COM's more ambitious cousin Marsec started out as a replacement for the former in guarding the martian colonies so that they could concentrate on potential alien threats, but soon becomes a para-military corporation with a ruthless reputation. Megapol from Apocalypse, in addition to being a police force, also operates other 24 hour services, the fire fighters and the hospitals.
 * Lensman Arms Race: As X-COM improves their arsenal and knowledge via research and reverse-engineering, the aliens will start sending bigger UFOs with larger groups of better trained soldiers wielding bigger guns with nastier support monsters, after which X-COM will improve their arsenal and knowledge via researching and reverse-engineering of anything this new wave had on their dead bodies. Rinse and repeat.
 * Les Collaborateurs: Repeated screwups in a particular funding nation or outright political manipulation thereof by the aliens can result in said nation cutting its remaining funding to X-COM and signing a nonaggression pact with the grey bastards.
 * Most annoyingly, when you spot a UFO or USO on a "diplomatic mission", if they've landed, you're already too late. You can assault the aliens, kill every single one, loot their ship and prevent any further incursions into that particular nation's airspace, and at the end of the month be told that they've signed a non-aggression pact with the aliens. Even if the ship was only on the ground for five minutes.
 * Lightning Bruiser: Mutons and especially the Lobstermen.
 * Made of Explodium: Some of objects on the battlescape will explode when shot.
 * Special mention goes to the Cyberdisc and its successor, the Bio-Drone. When they die, they explode, causing collateral damage. This can help for better or for worse, depending on who the explosion kills.
 * The weirdest Explodium is UFO Power Source. Each UPS of a crashed UFO explodes at "round 0" (after everything is spawned) with probability 3/4, obliterating unattended items (its Elerium), damaging terrain as if it was explosive with random strength of 180+(0-70), but leaving aliens caught in the blast either slain or completely unharmed randomly regardless of health (a puny Sectoid and Muton capable of surviving a Blaster Bomb in the face have equal chance).
 * Marathon Level: The two-parter missions.
 * Mercy Mode: Having a particularly bad month performance-wise or worse, a string of bad months, will make the game take pity on you by making the "X-COM agents discover the Alien Base". Technically possible even if you're doing fine, but much more common when you're doing bad.
 * Mind Control: the harder, but much more useful, use of psi powers.
 * Mind Probe: A handy tool for either side to gather information on the other. Best used for determining how close an enemy is to collapsing from stunning, or whether that alien right there is a Soldier/Medic (Mook), Engineer (useful for research), or a Commander (Boss, crucial to capture in the late game).
 * Becomes obsolete once you get high-psi strength units equipped with psi-amps, which can take total control of an enemy and allow you to see its stats at any time for the remainder of the turn, enough that you don't need to decide whom to try and disable and whom to shoot right away.
 * Monster Compendium: Via UFOpaedia.
 * Money for Nothing: UFO parts and corpses sell quite well and X-Com itself can self-finance through arms manufacturing.
 * The mind control devices sell particularly well. I wonder what use the prospective buyers would have for them...
 * Multinational Team: You recruit from around the world. However, recruit names are exclusively drawn from Russian, French, German, Japanese, and British/American pools (the last two being a little difficult to distinguish).
 * TFTD adds Spanish and Italian pools.
 * My Brain Is Big: The Sectoids and Aquatoids obviously.
 * Ethereals aren't exactly under-endowed in the grey matter department, either. Their design in Interceptor has a brain large enough to apparently need air-cooling.
 * And of course, the Alien Brain, UFO's equivalent to the Mother Brain.
 * Mythology Gag: Marsec first appearance was in X-COM's spiritual predecessor Laser Squad.
 * Nintendo Hard: At least two cases:
 * Psionic enemies before you get psionic troops (Mind control hell)
 * Any fight against a battleship when the doors on the bottom are propped open (by a dead body) or destroyed. One alien sees you, then blaster bombs will hit you.
 * Terror From The Deep in general. Because the (then unknown) bug in UFO Defense locking the difficulty to Beginner prompted the fans to complain about it being too easy, the developers made the Beginner setting of Terror from the Deep as hard as the Superhuman of UFO. There's a common rumour that TFTD had the original's bug backwards, locking difficulty to Superhuman. It doesn't; it's just a lot harder.
 * No Sell: HWPs or SWSs are robots/remote operated, and as such cannot be mind controlled or zombified at all.
 * Nor the Androids in Apocalypse. An extra benefit is that stupid Brainsuckers still turn themselves inside out trying to infect iron-heads. Which in itself is worth keeping an untrainable soldier in each squad - especially early on, when spamming of Brainsuckers is the worst threat in battlescape and many soldiers don't shoot well enough to pop them quickly.
 * Presumably, neither can the protagonist of Enforcer.
 * One of the novelizations has a guy who happens to have a Psi Strength of zero. It makes him unable to use psi powers at all but they don't work on him either.
 * Nothing Is Scarier: Night missions can be exceptionally creepy, especially in Terror From the Deep. It's pitch dark and there are aliens packing enough firepower to drop soldiers in one hit, and furthermore, since it's so dark, you don't know where they could be hiding.
 * It can get even worse if you're on a Terror Mission with Snakemen, and you know that there are Chryssalids just waiting for you to screw up.
 * Oh Crap: Not Enough Time Units! always comes up at the worst possible moment...
 * Open a door. Chryssalid in front of soldier. Try to shoot it. Not Enough Time Units! OH BUGGER!
 * Omnidisciplinary Scientist: The same staff of scientists does everything from reverse-engineering captured weapons to designing new aircraft to interrogating prisoners. Although considering that you NEED a lot of them to have a decent research progress, it could be handwaved that, say, a research on Plasma Weapons is led by the specialists in the field with everyone else following instructions.
 * In Apocalypse we got three types of scientists: Engineers, Quantum physics and Biologists.
 * One-Hit-Point Wonder: Your units actually have a life bar but, until they gain lots of experience or get some armor, they might as well have one hit point.
 * One Hit KO: Chryssalid melee attack. The same goes for its successors.
 * Soldiers can be easily killed in one hit from a Plasma gun, even if he is wearing a Power Suit, if the damage roll is high enough.
 * Vibro Blades in Terror From the Deep are capable of killing most aliens in one or two hits, including the Implacable Lobstermen.
 * One Stat to Rule Them All: Psionic Strength in the first game (and its cousin MC Strength in the second) is the only stat that cannot be trained and it determines both resistance to alien mind control and the soldier's ability to control aliens. Actively using psionic abilities provides experience for all but three other stats.
 * One Steve Limit: Averted due to limited names pool.
 * Only a Flesh Wound: Averted. Arm and leg wounds will greatly reduce a soldier's fighting ability, just like head and torso wounds. And that's on top of bleeding to death.
 * Organic Technology: All sorts of purpose-bred aliens in the first two games, and practically every aspect of the alien threat in Apocalypse.
 * Organization with Unlimited Funding: Averted at first, as the Funding Nations/Senate are huge cheapskates. But once you get enough engineering facilities going and cranking out weapons to sell, X-COM can effectively go rogue.
 * Player Headquarters: Though there is no HQ in the strict sense once you have multiple bases, the cost and time associated with building bases and the subsequent maintenance fees will make the first starter (and already developed) base your main base of operations.
 * Player Mooks
 * Powered Armor: Later armor suits in UFO Defense (and the whole lot of 'em in Apocalypse) use Elerium-115 to power shielding, muscle enhancers, and the occasional flight module. Flight and protection are the only benefits; armour has no bearing on a soldier's strength or other stats (the muscle enhancers are just fluff that indicates a lack of weight-related decrease in soldier performance).
 * Power Crutch: The PsiAmps and their variations that enable X-COM soldiers to use psychic powers.
 * Properly Paranoid: Anyone who takes great care while handling Terror Missions. If you aren't covering all the angles, you're just Tempting Fate.
 * Psychic-Assisted Suicide
 * Psychic Powers: Of the telepathic kind, making victims panic (or go berserk) to controlling them.
 * The second game renamed Psi to Molecular Control, which is suitably more horror-inducing.
 * Psychic Block Defense: There are only two aliens in Apocalypse that are easily affected by Psionics, them being the Anthropod and Skeletoid. All other creatures are resistant to Psionic attacks because they are either less intelligent (which somehow boosts resistance), in the case of Multiworms or Spitters, or possess Psionic abilities themselves, like the Micronoid Aggregate and Psimorph.
 * Purely Aesthetic Gender: Recruits can be either male or female. This has absolutely no effect on starting stats or stat growth. All it does is paste a slightly different head on the sprite and give ladies a different scream when they die.
 * Randomly Generated Levels
 * Random Number God: See Armor Is Useless trope above.
 * Real Time Strategy: During the Geoscape\Cityscape.
 * Red Eyes, Take Warning: The Reapers in UFO, the Aquatoids in Terror from the Deep.
 * The Red Planet: Alien HQ in UFO, colonized by humans after TFTD and is the humanity's main source of elerium-115.
 * Red Shirt: The default state of every X-COM recruit. Turning them Mauve is a Luck-Based Mission in itself.
 * Not quite a challenge since you can abuse Save Scumming. Once you have those psi devices, you can make the aliens throw away their guns and turn them into target practice for your new recruits.
 * The reboot changes recruits for the player's squad into actual people with their own skills and backgrounds. Some prefer the old way.
 * The Sectoids and their successors could easily be the aliens' redshirts, with the exception of Leaders, who possess psychic powers.
 * Redshirt Army: What you start the game with.
 * Ridiculously-Fast Construction: Building a base gives you an instant lift. Other than that, the game avert this.
 * Roboteching: Blaster Launchers and their equivalents with their diabolical waypoint-based targeting system.
 * Save Scumming: a common strategy, unless you think this is cheating or dishonorable, it is possible to win the game with 0 casualties.
 * Sensor Suspense: Motion detectors: a good way to avoid becoming Cannon Fodder when facing alien weapons, but since you don't know whether the blip is from alien or civilian and on which floor, dealing with the results can be... interesting.
 * Two words: Hidden Movement.
 * Scary Dogmatic Aliens: Of the Conqueror type.
 * Self-Imposed Challenge: Probably the greatest fan-mod undertaking for UFO Defense is fixing a bug that locked the starting difficulty of the game at "Beginner".
 * There are a bunch of challenges listed with one of the well-known editing utilities, including things like refusing to research any new tech (thus making the game technically unwinnable, but few get to such a point since it's damn difficult without) and not killing any aliens (winning is still possible since they can be stunned).
 * Zero loss run: No X-Com agents lost, no civillians lost. Hope you have a few months spare.
 * One Mission X-Com: It's possible to complete the game after completing only one mission: a well-executed UFO Ground Assault on a battleship can yield all the alien prisoners and raw materials needed to research Cydonia and complete the game. The difficulty is in pleasing the Funding Nations (no terror missions or alien base assaults allowed), and in keeping away from bankruptancy.
 * Sequel Stagnation: Averted. After Terror From The Deep, which was basically an underwater rehash of the first episode, new elements and even Genre Shifts were introduced - unfortunately, they didn't result in good games.
 * Shiny-Looking Spaceships: UFOs of the first game. X-Com fighters in Interceptor.
 * Smoke Shield: Caused by specialized smoke grenades and explosive terrain features.
 * Sorting Algorithm of Evil: In UFO Defense it's Sectoids and Floaters and early Snakemen if you're unlucky > Snakemen if you're lucky > Mutons > Ethereal.
 * In TFTD it's Aquatoids and Gillmen > Tasoth and Lobstermen.
 * Also lampshaded in Guava Moment's Apocalypse LP.
 * Spiritual Successor: Many. The UFO: After Blank trilogy to name one.
 * Springtime for Hitler: It's more or less and Open Secret that Interceptor and definitely Enforcer were this on Hasbro's part, having bought up Microprose simply to eliminate competition and intentionally running the acquired IP into the ground rather than shift focus away from their own core works.
 * Splash Damage Abuse: The great vulnerability of ground-based vehicles in Apocalypse, including the tank. Also, most units take more damage from explosives that go off at their feet because of lower under armour.
 * Strong Flesh, Weak Steel: Individual soldiers, in the late game, are far stronger than tanks, since soldiers improve their stats and tanks don't.
 * Inverted in Enforcer, where you will chew through Sectoids, Snakemen, and Chryssalids with one shot each while their feeble attempts to harm you bounce off your armored hull. It will give your positronic brain much amusement.
 * However, a hovertank/launcher can still fire fusion balls without ever needing to reload until they run out of ammo. Although, this is balanced out by having a maximum of 8 fusion balls per mission and doing less damage than blaster bombs. Also, tanks can't be stunned or get fatal wounds. Or Mind Controlled.
 * Stat Grinding: Psionic actions are a great shortcut for all but a few stats.
 * Stock Sound Effects: Some of the sounds that occur while navigating the menus of the original X-COM have spread far and wide across various media, recently being used in the title character's HUD in the big budget movie Iron-Man!
 * Stun Guns: From Stun Rods to Stun Bombs, a variety of nonlethal arms gradually come into X-COM's possession and employ for the capture of necessary live aliens.
 * Subsystem Damage: Head, Body, Separate Arms and Legs, with penalties one soldier's efficiency depending on injuries. Assuming the soldier in question survived the first shot.
 * Super Soldier: Mutons and Lobstermen. Your soldiers will become this if they are lucky enough.
 * Enforcer's protagonist, who racks up over a hundred dead aliens a mission, and sometimes as many as four hundred fifty.
 * Tactical Withdrawal: When the situation gets hopeless on the battlefield there is a option of retreating. The good side of this is that your soldiers live to see another day, the sponsors will be less angry than with total defeat and thus complete loss of expensive equipment, and that you could yoink some alien artifacts. Just be aware that everything that was outside the X-COM transport will be lost and MIA.
 * Take Cover: Very important, given the computer's cheating tendencies and the power of alien weapons. Unfortunately, most forms of cover can be destroyed.
 * Concealment Equals Cover since all objects can stop at least one shot. Shame aliens tend to fire on full auto.
 * Tank Goodness: HWPs are a refreshing alternative to the hopeless rookies in the early game, at least in Enemy Unknown.
 * It gets better in TFTD. SWSes do make good scouts if you don't like sacrificing rookies for that. Once you get a Sonic Displacer, you will like it for its ability to float, get 200 shots clip which gets reloaded for free every missions, and ultimately, SWSes can't be harmed by tentaculats. If you already have the bigger ships, you will always want to bring one (or two) on every missions.
 * Team Title
 * Tech Tree: While almost all physical alien artifacts can be researched as soon as you recover them, several conceptual lines of research require either the interrogation of live aliens or a series of prerequisites.
 * Telepathic Spacemen: Ethereals, experienced Sectoids, their underwater cousins Aquatoids, Gill Men commanders, Tasoths, Psilords in Interceptor, the list goes on...
 * Throw Down the Bomblet: Grenades are better or worse for various reasons in different games, but at very least it's an indirect attack (usually the only one available) and can be done without triggering reaction fire (if the grenadier is not in line of sight of an enemy). It uses a separate attribute (except in Apocalypse), allowing the agents who can't shoot straight to be useful beyond point-blank range.
 * Time Keeps On Slipping: The various incarnations of the Geoscape allow you to pass the time by anywhere from 1 second per second (slowest setting in Apocalypse) to 1 day per second (fastest setting in UFO Defense and Terror From The Deep) while you're waiting for the next alien sighting.
 * Turn Based Tactics: The Squad-Level type during the battlescape.
 * Unobtainium: Elerium-115, in spades. Ununpentium has long been theorized to work that way, but currently doesn't. Also, Terror From The Deep's Zrbite.
 * Unusable Enemy Equipment: Which will become usable after research.
 * Unfriendly Fire and/or The Uriah Gambit: Note that the post-mission analysis does not have a spot for "X-COM Operatives Killed By X-COM Operatives." Your use of this oversight to justify friendly fire or the immediate court-martial of an alien-controlled operative will practically be a given.
 * Urban Warfare: Terror missions. Most of Apocalypse.
 * Video Game Caring Potential: Just TRY not to get attatched to your soldiers who got promoted to Sergeant or above rank. I dare you to.
 * Video Game Cruelty Potential: What happens if you make a bunch of rookies designed explicitly to be cannon fodder and/or scouts (yes, the two jobs overlap frequently). This makes for some delicious Black Comedy as you can name the unfortunate saps such names like "Dead Man Walking" and "Cannon Fodder."
 * Vendor Trash: All those alien corpses, spare UFO/USO compoments, and ammunition? Yeah, a good deal of that gets sold off to finance the organization. Even a relatively small UFO captured intact can net nearly a million dollars depending on how much loot you hold on to. Alien corpses are often extremely convenient for research, but supply exceeds all possible demand, so selling them is a non-trivial but disturbing source of income. (A strategy guide suggests that they make for excellent sushi. And a certain fan wiki suggests that bases frequently fighting Lobstermen requisition above-average amounts of butter.)
 * To be fair, they do the same to us in the first place. They deserve every bit of what the scientists and chefs do to them.
 * Lampshaded in Jade Star's LP of UFO: Aftermath. Mmm, Reticulan Burgers...
 * Some mods added possibility to "disassemble" for implants corpses of heavily cyborgized aliens - especially Floaters, as an alternative path to get flying armor.
 * The Very Definitely Final Dungeon: The various Aliens' HQs. Failing the missions results in instant gameover.
 * Veteran Unit: The Lucky Soldiers who survived enough battles and killed enough aliens.
 * Vichy Earth: Earth slowly becomes this over the course of the game if you do badly or take too long, as more and more countries submit to the aliens.
 * Apart from Glorious Mother Russia. Fan studies of long-term games have concluded that out of the Council of Funding Nations, Russia will never be infiltrated by aliens. The newspapers will instead probably show Sectoid ambassadors' corpses nailed to the gates of Kremlin.
 * "Heh, they call that BIG?"
 * The War of Earthly Aggression: Mentioned in the backstories of Interceptor and Apocalypse.
 * We Have Reserves: Rookies make good scouts.
 * The game mechanics actually encourages a We Have Reserves mentality. If you feed TFTD rookies to keep it happy, the game can be quite manageable... but if you've truly mastered your tactics and so almost never lose a man, you're screwed.
 * This mentality is sort of averted in Apocalypse. If you're good enough to consistently keep your squads alive in the early game, the difficulty will scale up quickly, but the aliens will be getting better weapons before better units (and an Anthropod holding a Devastator Cannon is still just an Anthropod), so if you really are that good, you can stay on top of the game all the time.
 * The death of a rookie is less damaging to a squad's morale than the death of a higher ranking agent. And if you're feeling particularly cold, the aversion of Easy Logistics makes it a lot easier, and cheaper, to send rookies in to combat with a bare minimum of equipment so that higher ranking and more skilled agents can get the good stuff.
 * We Sell Everything: Played straight for most of the series.
 * It makes one wonder what the people do with the alien artifacts you sell, especially the corpses.
 * With This Herring: With this bunch of folks who would have failed the physical for any self-respecting military and have the reflexes of a dead fish, you must save the world...
 * The standard-issue X-COM rifle is supposedly based on the best traits of a variety of human firearms, combined into one package perfect for your work. Unfortunately, it was built by the lowest possible bidder.
 * Played even straighter in Terror From The Deep. The standard equipment you get is worse than their UFO counterparts, and about half of them only work underwater.
 * Despite that fact that "Starlight" night vision scopes and binoculars have been available since at least the Vietnam War and passive infrared night vision has been around since the 1980s...you're reduced to throwing flares.
 * Who You Gonna Call?: Type 3, the Organization.
 * Yet Another Stupid Death: Players who are unlucky, forget to take precautions, or just play poorly, will get lots of these. Even a seasoned player will have some of these from time to time.
 * You All Look Familiar: A good number of soldiers will have similar appearances on the inventory screen. Played Straight in missions. On the map they virtually all look alike. The guys all have Guile haircuts and the women have ponytails. Ditto for civilians.
 * Zerg Rush: The only straightforward way to take a small alien ship in Enemy Unknown (without explosion leak exploit) is to keep pushing soldiers through the door until you kill everyone inside. This will almost certainly cost you several troops. On a larger scale, X-Com typically has extremely high casuality rates in all three games and Zerg Rushing strategically to replace lost soldiers and interceptors is the only way to keep your head above water.
 * One-robot Zerg Rush is probably the best way to play Enforcer, as it lets you get those research points.
 * You can take down the largest UFOs in Apocalypse using the smallest flyer available: Hoverbike, preferably with upgraded engines. They are practically impossible to hit. Worked for the Rebels. The city catches most missed shots, however.

UFO Defense/Enemy Unknown (1993)

 * Achilles' Heel: The Sectopod is encountered late game when Ethereals start to show up. According to the game, they have some kind of energy shield that protects it against Plasma Weapons. However, a crippling design flaw in their shielding makes them vulnerable to Laser Weapons.
 * The Aesthetics of Technology: The alien technology is sleek, shiny and spotless.
 * Alien Lunch: The "Alien Food" is a nutrient soup made from body parts extracted from cattle and humans. You can even sell it on the market.
 * All Deserts Have Cacti: Any desert you visit in UFO Defense has Cacti. Even the deep Sahara or the Rub al Khali. Even the desert in Enforcer has cacti.
 * Animesque: The intro of the UFO Defense is proto-animesque, and the demo's list of features mentions a "popular "Manga" look and feel to graphics." Otherwise, the graphics are about as realistic as can be expected from a game of it's age.
 * Anticlimax Boss: The Alien Brain at the tail end of UFO Defense. See the page for examples of just how pitiful the final fight can get.
 * Apocalypse How: Class 2: if you fail to stop the aliens, they take over the world, destroy human civilization completely, and humanity ends up as a race of semi-intelligent mutants at best. Also, the sky burns.
 * Armless Biped: The Reapers.
 * Artificial Stupidity: Aliens don't pick up equipment they dropped when panicking and walk over it unarmed. Even though there's code handling this. See, there's a property controlling whether item is picked up, but apparently it was changed from boolean to number - items are picked up if value is ≥ 5 (while standing on top of it, i.e. lower values of attraction can make sure aliens don't chase grenades thrown by their pals, while e.g. a pistol may have greater value, so AI would walk over there), but all the items are assigned 0 or 1. Oops. Various unofficial patches handle this matter.
 * Briefcase Full of Money: a picture of a high-ranking XCOM agent with one of these and silhouettes of obviously armed guards behind him is the background for the screens for the buying/selling and hire/sacking of personnel.
 * Cool but Inefficient: Fusion Hovertank. Sure, it lobs powerful guided missiles... wait... wasn't the main advantage of waypoint walking weapon its ability to attack from behind several corners without facing any enemy fire, while the primary purpose of HWP is being tough enough to absorb some shots without visiting hospital later? It can shoot every round, but takes the place of 4 soldiers, who could have 4 Blaster Launcher shots per 2 rounds - 2x average or 4x peak rate of fire. The only actual advantage here is squeezing better into arbitrary item number limit. The worst: HWP Fusion Bomb is only marginally weaker than Blaster Bomb, but it's enough that it cannot breach hull... oh, and it's almost twice as expensive to make ($15000 + 400 hr + 5 Elerium vs. $8000 + 220 hr + 3 Elerium).
 * Covers Always Lie: The European cover art depicts insect-like aliens which do not appear in the actual game.
 * Cutscene Power to the Max: Inverted - the opening animation of UFO Defense features troops facing down Mutons with Personal Armor, a couple of the beginning rifles, and an Auto-Cannon. By the time you normally face Mutons, however, you'll be trampling them with Powered and Flying Suit-equipped soldiers packing any combination of Psi-Amps, Laser Rifles, Heavy Plasmas, or Blaster Launchers. Even if not, rifles will be obsolete both by this time and against Mutons in general.
 * Played straight in that you will get your ass kicked.
 * Amusingly played straight in that you will never see that red-suited Muton in the game: there's only one green sprite set for them. For that matter, Mutons have no Commanders or Leaders (or even Medics).
 * Drone of Dread: The battlescape soundtrack is a constant, low, pulsing drone.
 * Dummied Out: At least, several weapons and UFOs (having Snakemen fly in those pyramidal ships would be cool).
 * Dynamic Entry: Nope. More like "Stick Your Head In The Meatgrinder" Entry. Often ends up with rushing over the corpses of those who entered first and caught reaction fire.
 * On the other hand, most of the aliens will leave their ship and actively hunt for you starting with the 21st turn. Camping their ufo doors lets you snipe them as they poke their heads out.
 * Another popular tactic is to have a couple of throwers with proximity grenades mine the UFO's entrance while the rest of the squad hunts down any aliens outside. After turn 21 you can just sit back and watch the show as the aliens walk out into the minefield. The downside is that since you mine the choke point, following explosions will destroy the loot. Often it's possible to use motion sensors to make sure no one is close to the door and send dedicated gophers to evacuate loot before dropping the next mine, but what to do if there are more of them around?
 * A less wasteful approach is to use one mine first, then pour incendiary around the exit and keep some observers where they won't be easily shot; when the aliens walk out, take potshots from long range, preferably from behind (they often move toward the corners), including more incendiary.
 * It's also possible, with careful Time Unit management and a sizeable slice of luck, for one or two of your team members to toss in a grenade and get out of the line of fire in a single turn. Unreliable tricks involve things like sending a soldier with high reaction and tossing a smoke grenade after him. With luck, he will be blocked and shoot first when aliens approach.
 * If you have blaster launchers, you can make your own door, and if you have stun bombs, exploit to stun that soldier, leaving an unobstructed doorway for the rest of this round. At the start of the game, you have neither.
 * OpenXcom allows to open doors without walking through them (if you activate "Alternate movement methods" option).
 * Fantastic Drug: Sort of. Some UFOs have weird rooms with walls that look like their covered by shifting blue or orange clouds. These rooms are revealed to be a form of alien entertainment that stimulate certain sensory regions of the brain. They are described as being similar to hallucinogenic drugs.
 * Flying Saucer: One of the smaller alien craft in the first game take this form, as does the first X-Com built craft. The Cyberdisc is essentially a miniaturized flying saucer with a powerful plasma cannon.
 * The hovertanks appear to be based off the cyberdisk design. As in, they just look like repainted cyberdisks with a tank cannon mounted on top.
 * Essentially every UFO is a variation of a Flying Saucer.
 * Kill It with Fire: Kind of tricky, since incendiary does very little damage ("damage" numbers actually affect only spread), but has perks - starting with non-lethal hits making the target provide illumination on itself and everyone around. On the other hand, a bug causes all fire and smoke to apply damage every time incendiary goes off anywhere. Burning the zombies with incendiary ammunition will also kill the chryssalid/tentaculat without it popping out. Reapers are more vulnerable to fire, and for big units in general, each of 4 tiles caught in the blast takes damage from fires and explosives - it simply adds up. Also, it's one of the ways to kill a Cyberdisk without tripping its self-destruction.
 * Next Sunday AD: The original game was released in 1993 and set in 1999.
 * Novelization: Has had at least two: One by Diane Duane and one by Russian sci-fi author Vladimir Vasilyev.
 * Obvious Beta: Far from the worst, but generic item names, placeholder values (like "everything 1-square is Weight 3", including Proximity Grenade more powerful than a basic grenade without being heavier), lots and lots of bugs - tanks flip out due to massive losses crashing the game, items turning into proximity mines, "Last Shot Always Misses" interception sequence bug, many map errors... and something as trivial as item data file not updated for the new system for AI picking up items.
 * Plunder: Oh, yes. You need that juicy alien stuff. Especially their Elerium - the only thing you cannot buy or make. But in a crash-landed UFO every Power Source has 3/4 chance to be destroyed - along with its Elerium. Thus it may be more dangerous, but more profitable to let UFO land and then engage. It will be a problem if UFO was on Terror or Infiltration mission (and maybe Base - depending on the location, aliens' race and game situation),of course. But with Supply ships the game promotes this approach: they are impossible to catch using Terran aircraft, but they always land, and then... we board this scow, mateys. Arr.
 * Elerium "under" UFO Power Source will be vaporized by a grenade 2 steps away, but UPS itself can take it even at ground zero... which means there's a whole science to raiding alien bases for loot without destroying - they re-spawn said cool stuff inside, and generate regular missions with big fat supply ships, that are easier to pick than terror sites and/or battleships (no terror units, for one).
 * Reptiles Are Abhorrent: The Snakemen.
 * Roboteching: The blaster launcher is a missile launcher that sends it payload to a series of player defined waypoints, making any absurd trajectory possible. However, since the missile can't hit its waypoints with perfect accuracy, the most effective way to use it is to set a waypoint twenty feet above an enemy's head, then another waypoint directly on the enemy, causing the missile to arc over the target, then slam down, ensuring it will explode even if it misses.
 * Saffron Cloak: The Ethereals.
 * Shout-Out: The leader of the aliens is a huge Alien Brain that controls their Hive Mind, not so different from Metroid's Mother Brain.
 * Shut UP, Hannibal: UFO Defense's ending.
 * Slasher Smile:
 * The Chryssalids have one permanently. Fitting, really.
 * Snakemen have a big toothy grin as well, but then again, they don't have any visable lips.
 * Slippy-Slidey Ice World: Arctic and Antarctic missions, thankfully without the slippy slidey part.
 * Squishy Wizard: Ethereals' bodies have atrophied so much that their self-sustaining functions have to be governed by their immense Psychic Powers. Which does not prevent them from having the best armour values and second best hit point totals among the non-terror unit aliens.
 * Their huge cloaks present a considerably larger profile then their actual bodies...hitting the cloak is not necessarily hitting the Ethereal. Plus, there isn't much to damage in their bodies.
 * BUT, their brains still need an ample supply of blood, and if they lose too much blood because of serious injuries, they die.
 * Throw Down the Bomblet: Starting stats are a bit funny, in that usually half of your soldiers have troubles hitting a barn on full auto, and half of those happen to be basketball gods, with the rest still fairly good. Equipping them as grenadiers until their shooting improves is just common sense.
 * Trick Bomb: Proximity Grenade.
 * The Very Definitely Final Dungeon: The aliens' Martian base located in the Cydonia region.
 * Weaksauce Weakness: Speaking of Sectopods, their primary weapon counts as a laser attack (which they're weak to), even though it looks like a plasma attack. Combine that with the fact that 2x2 enemies have to be mind-controlled one block at a time and that blocks controlled by opposing sides can fire on one another...
 * Controlling part of a Cyberdisk or Sectopod is, in fact, the easiest way to destroy one. It's enough to move, and the other 3 quarters will reaction-fire at it if they have TU.
 * Flying suits will bring aliens with melee only attack - including the fearsome Chryssalids - at your mercy.
 * Controlling part of a Cyberdisk or Sectopod is, in fact, the easiest way to destroy one. It's enough to move, and the other 3 quarters will reaction-fire at it if they have TU.
 * Flying suits will bring aliens with melee only attack - including the fearsome Chryssalids - at your mercy.

Terror From The Deep

 * Achilles' Heel: Lobstermen and Triscenes are both hard to destroy and survive several hits from the most powerful weapons. Lobsetermen survive hits due to massive damage reduction despite light armor, and Triscenes rely on their heavy armor. However, they both have a weakness. Lobstermen are vulnerable to stun or melee attacks, and Triscenes have a weak underbelly that won't protect against grenades.
 * The Aesthetics of Technology: Aliens have a Used Future look.
 * Alien Popsicle: The aliens used cryogenic stasis chambers to remain dormant for thousands of years. You can also sell these chambers as Vendor Trash.
 * Animal Motifs: The smaller USOs have a manta-like design.
 * An Ice Person: Hallucinoids are prehistoric jellyfish that were modified to use a powerful chemical freezer. They attack by using a melee attack that literally freezes targets to death.
 * And I Must Scream: And the sonic screams of the Bio-Drones are very, very painful.
 * Apocalypse How: Class 3: Failing to stop the aliens means their city-weapon rises from the deeps and kills pretty much everything.
 * Armless Biped: The Triscenes.
 * Armor-Piercing Attack : While there is an "Armour Piercing" damage type, they aren't good at penetrating armor. This job instead applies to Vibro Blades, Thermic Lances, and Heavy Thermic Lances. While you can kill the absurdly heavily armored Lobstermen without them (they take a maximum of 50% damage from most sources), once you realize that they take 200% damage from those weapons, you'll be carrying them with you everywhere.
 * Artificial Stupidity: Are any of the aliens in a given mission equipped with Sonic Pulsers? They'll also be carrying either a Vibro Blade, Thermic Lance, or Heavy Thermic Lance - and yet they never use them, even if they've run out of Sonic Pulsers.
 * Aquatic Mook
 * Bag of Spilling: X-COM was disbanded after the First Alien War thanks to politics of funding nations, reduced to the underwater Elerium salvage team financed by a tycoon, until the arrival of aliens prompts the nations to resume funding.
 * Blob Monster: The Calcinites, although they were contained in a humanoid diving suit.
 * Boarding Party: The Ship Terror Missions.
 * Brain In a Jar: The Bio-Drones.
 * Cloning Blues: Just about all of the aliens are cloned.
 * Derelict Graveyard: Small ones when recovering USOs.
 * Diesel Punk: The aliens show elements of this.
 * Divided States of America: People's Republic of Alaska.
 * Dronejam: With the addition of narrow pathways (e.g. having to climb a tower in a city, or entering an underground bunker in Moai), civilians will now block the player and have trouble getting out of the way.
 * Eenie Meenie Miny Moai: They show up on island terror missions in TFTD. Must be some kind of fad in 2040.
 * Eldritch Abomination: The Big Bad is the sleeping one from T'Leth, and he waits.
 * The UFOPaedia describes the Tentaculat as something not even the depths of a Lovecraftian nightmare could spawn. From its truly alien appearance and abilities, many players would agree with that verdict.
 * Everything's Harder With Heavily Armored Cyborg Dinosaurs With Mounted Sonic Cannons.
 * Fish People: The Gillmen.
 * Also, the Lobstermen.
 * Flying Saucer: What do you get when you take the cyberdisc, miniaturize it, waterproof it, replace the CPU with a still conscious human brain and replace the plasma cannons with a concentrated sound wave generated by said brain's reactions to the inherent agony of the process? The answer is: The Bio-Drones.
 * There's also the Dreadnought, TFTD's answer to UFO's Battleship, which almost looks exactly like its UFO counterpart, in that it looks like a giant Flying Saucer.
 * Game Breaking Bug: Never research the Tasoth Commander.
 * If an explosive object is detonated by a stray shot from a Deep One, the aliens will freeze up and their turn never ends.
 * Giant Enemy Lobsters: The much feared Lobstermen.
 * Until you acquire flying suits and mind control. As they are invulnerable to basic pistols, they become the best target practices.
 * Or, when you get Vibro Blades.
 * Glass Cannon: The Tasoths are a varient of this. All Tasoths have potent M.C. abilities, but on lower difficulties, aquanauts with high enough M.C. stats can easily use mind control on them.
 * Deep Ones possess an attack that can kill an aquanaut in one hit, regardless of armor, but are fairly easy to kill.
 * Harpoon Gun: Your starting "standard rifle". And it sucks hard.
 * Hot Sub-On-Sub Action: Your subs versus USOs.
 * Humanoid Abomination: The Deep Ones.
 * If It Swims, It Flies: USOs (Unidentified Submersible Objects) and your flying subs that intercept them. Both can fly over land, but your subs cannot fire unless underwater.
 * It would've been nice to bring in local air forces and then recover the wreck on land with leftover laser weapons.
 * Not only that, but why can't you use Gauss Cannons or Sonic Oscillators on land either?
 * Implacable Man: The Lobstermen. They. Will. Not. DIE.
 * Let's put it this way... unless you drop them with the heaviest melee weapons, chances are, they're actually unconcious, not dead.
 * Not really. Sonic Weapons can have a good impression on them, and a few good shots with a Sonic-Blasta or Sonic Cannon can drop them.
 * The Triscenes are Implacable Dinosaurs.
 * Kill It with Fire: Much the same as in the first game. Burn a zombie, and the Tentaculat won't pop out.
 * Kill It with Ice: Subverted. Freezing weapons, including Thermal Tasers and Thermal-Shok Bombs, are the equivalent of Stun Weapons from Enemy Unknown. Instead of killing targets, they harmlessly freeze them, allowing you to capture aliens.
 * Lethal Lava Land: Sort of, one of the TFTD combat mission terrains consists of underwater mini-volcanoes leaking cooled lava. They have no effect on your soldiers and enemies, but they do provide illumination in night missions.
 * Lizard Folk: The Psychic Tasoth.
 * Lost Colony: T'Leth is a massive colonizing ship that crashed 65 million years ago.
 * Make Me Wanna Shout: The Aliens' Sonic Weapons, TFTD's equivalent of UFO's Plasma Weapons. Bonus points for the Bio-Drone, whose sonic beam is based on the original vocal cords of the brain that pilots it, meaning that it literally screams its enemies to death.
 * No Ontological Inertia: Killing the Big Bad and destroying T'Leth makes all the remaining Zbrite inert, only good enough in large numbers, which is how they managed to send an Avenger to Mars for E-115 prospecting.
 * No Waterproofing in the Future: Weapons and other technology developed (or reverse-engineered) during the decades of fighting in UFO Defense are completely useless underwater, so, in Terror From The Deep, you must restart the researches from scratch. Consider it a Justified Bag of Spilling... that is, unless you're a clever enough hacker to exploit the similarities of the UFO Defense and TFTD engines and carry over goodies whose quantities were stored in the same data addresses.
 * Partially justified by the fact that the alien gear needs Elerium, and the rest of the stuff is lasers. Still doesn't explain why they don't keep a few crates of lasers around for land missions, though.
 * Phlebotinum Killed the Dinosaurs: The Colony ship T'leth crashing on Earth is what killed the dinosaurs.
 * Punctuation Shaker: T'leth.
 * Recycled in Underwater
 * Reptiles Are Abhorrent: The Tasoth.
 * Running Gag: A small one amongst veteran Terror players is that bases which see regular combat against the Lobstermen often requisition suspiciously large amounts of butter.
 * Sealed Evil in a Can: The Big Bad is one, not suprising since he is an expy of Cthulhu.
 * Sequel Difficulty Spike: Early versions of the first game had a bug that enforced low difficulty mode. Due to player complaints, the sequel had the challenge rating cranked up - sure the bug was gone, but even "easy" mode was a fair challenge without Save Scumming.
 * Ship Level: The Cargo/Cruise Ship Terror Mission. They consist of two parts, above deck and below deck, like Cydonia. Plus numerous rooms, narrow corridors and lots of hiding places and you got a recipe for disaster.
 * Shout-Out: The Calcinites in bear a laughable resemblance to the titular antagonist of the B-movie Robot Monster due to them impersonating old-school divers. Enforcer also features a mishmash of resources from two fellow X-COM titles scrapped during its development, Genesis and Alliance.
 * TFTD is practically made of shout outs, if not direct ripoffs. The Tasoth race are pretty much Lovecraft's Deep Ones (even though there's an entirely different race in the game actually called "Deep Ones"), especially since their original description (which was replaced in the final version of the game) had them being converted humans (much like the aforementioned actual Deep Ones of the final game). The Gill Men are extremely similar visually and thematically to the Gill Man of Creature From The Black Lagoon, as well as being very reminiscent of the Sea Devils and Silurians of Doctor Who. The Great Dreamer, leader of the aliens, who sleeps most of the game away in the sunken spaceship/city called T'leth is, when you finally see him, an expy of Cthulhu, that giant monster/god dude who's slept away most of history in the sunken city called R'lyeh. Oh, and the Tentaculats are, visually, a copy of D'n'D's Grells, but a lot of that sort of thing went on in the early 90's (Doom's cacodemon is almost a direct rip of the artwork for an extraplanar D'n'D monster, for instance, and a good number of landscape tiles from the first two Duke Nukem games are ripped from other platform games from other companies).
 * Space-Filling Empire: The Nations in 2040, Including:
 * Middle-Eastern Coalition: Arabic Bloc.
 * United Europe: Euro-Syndicate, with the exception of Northern Europe which formed it's own united state (Scandinavia) and Icelandic Union.
 * Technology Marches On: CRT monitors in 2040 and much more.
 * This Is a Drill: The game features a series of power drills that are the most effective weapons against Lobstermen. Combine with Molecular Control Disruptors to conserve ammo, or Thermal Shok Launchers/Thermal Tazers if you need to take them alive.
 * Ultraterrestrials: The Gillmen are native to Earth.
 * Under the Sea: Half of TFTD is this.
 * Underwater Base: X-Com's base of operations. Also, one of the rarer terrain type in the USO recovery missions is a small series of underwater modules.
 * Underwater Ruins
 * Unwinnable: The state of game in which the Tasoth Commander has been researched. Thankfully, patches and mods keep this (and other deadly bugs within the Tech Tree) from happening.
 * Used Future: The Aliens seems to give this vibe.
 * The Very Definitely Final Dungeon: The Colony Ship of T'leth.
 * Vibroweapon: The drills.
 * Water Is Air: The Terror from the Deep was directly adapted from the original with no changes, so the characters are able to do ridiculous things like throwing grenades underwater. They also are unable to float or swim (instead just tromping around on the ocean bottom) until you research the equivalent of the flying suit.
 * On the Geoscape, there are times where your fighter craft/troop transport cannot engage/deliver soldiers due to the (downed/landed) USO being "too deep", presumingly because of water pressure.
 * Weaksauce Weakness:
 * Tentaculats: Unlike the UFO Defense counterpart which can damage tanks, Tentaculats can't damage your SWS, and will still stupidly try to attack them anyway to no avail. So always bring one if you are expecting them.
 * Lobstermen: While even the alien's own Sonic Cannons can barely scratch them, they are surprisingly vulnerable to both melee attack and thermal weapons - if you haven't got the Vibro Blade line of research opened up yet, make sure you pack some Thermal Tazers and/or Thermal Shok Bombs.
 * Triscenes: They can take some Sonic Cannon punishment, but its non-existent underside armor means a single cheap magna-blast grenade thrown under it will most often kill it.
 * Xtreme Kool Letterz: The Sonic-Blasta Rifle and Thermal-Shok Bomb Launcher. Sounds Orky enuff?
 * Triscenes: They can take some Sonic Cannon punishment, but its non-existent underside armor means a single cheap magna-blast grenade thrown under it will most often kill it.
 * Xtreme Kool Letterz: The Sonic-Blasta Rifle and Thermal-Shok Bomb Launcher. Sounds Orky enuff?

Apocalypse
"Director Zander: Oh please tell me that's not a fifty-foot monster."
 * Abnormal Ammo: Brainsucker Pods for the... Brainsucker Launcher.
 * Also, the Entropy Launcher: A bioweapon firing homing missiles which release a compound that will dissolve carried objects, including armor. A soldier can survive the hit itself, but ends up without armor and with hands full of ammo and grenades that go off when destroyed. Dropping anything that explodes and running from it helps - but without armor, the sensible thing to do next is to try and reach the nearest map exit without being shot.
 * Action Bomb: The Poppers.
 * The Aesthetics of Technology: The Aliens and their technology are organically ugly. The Mega-Primus city regulations mandates that everything should look retro-futuristic, which is most noticeable on flying cars.
 * Anti-Air: Various weapon modules for the ground vehicles.
 * Another Dimension: The Alien Dimension.
 * Apocalypse How: Class 4,.
 * Armless Biped: The Poppers.
 * Attack of the 50-Foot Whatever: The Overspawn.
 * Attack of the 50-Foot Whatever: The Overspawn.


 * Bee People: The Aliens.
 * Blob Monster: Micronoid Aggregates.
 * Cult: The Cult of Sirius, who believe that the Aliens are the saviors of humanity.
 * Decapitated Army: Averted, you have to destroy the entire alien infrastructure to win.
 * Deflector Shields: Disruptor Shields, for both individuals and vehicles.
 * The Dev Team Thinks of Everything: Selling a large amount of alien weaponry will result in it showing up in the hands of the various factions in the city, which can be either a very good thing or a very bad thing depending on your relationship with those factions.
 * Do Well, But Not Perfect: If you're very, very good, the Senate will decide that you're very cost-efficent and will reduce your weekly funding.
 * Enemy Mine: Factions have a matrix of relationships, and an attack on given faction will cause those who are more hostile to the target to support the attack. If attacking aliens causes relationships to decrease with other corporations, then they like the aliens a bit more than they like X-Com.
 * Fictional Political Party: Major parties of Mega-Primus Senate in are Not So Different rivals Extropians and Technocrats.
 * Flaming Sword: The Power Sword, a powerful blade weapon that is enhanced by a Elerium-powered plasma sheath.
 * Flying Car: Relatively common vehicle type in Apocalypse.
 * Fun with Acronyms: The fact that a robots' rights group in Apocalypse would call itself the "Sentient Engine Liberation Front" clearly indicates that they deserve more credit than they're given.
 * Guns Akimbo: The Real Time combat mode allowed this - oddly, turn-based did not; carrying two guns penalized accuracy and only let you fire one at a time. Whilst troopers suffer (sometimes considerable) accuracy penalties for dual-wielding certain large weapons, it's quite feasible to use two autocannons at once if one so chooses. With a bit of tweaking for fully automatic fire and large magazines, you really have to be careful with that Explosive and Incendiary ammo.
 * Hero Insurance: Averted, you pay for the collateral damage.
 * Invisibility: The Personal cloaking field.
 * Just Before the End: The aliens invade from a doomed, volcanic planet in another dimension where most other life has been scorched away by the local star's supernova.
 * Mega City: Mega-Primus itself, obviously.
 * Mega Corp: About ten major ones in Apocalypse, among a few others it'd probably be a good idea to defend against alien infiltration.
 * Mob War: Rare, but happens sometimes.
 * New Neo City: Neo-Japan.
 * The Nudifier: The Entropy Gun in Apocalypse. It's a homing bio missile which, on hitting, starts to dissolve all your armour and weapons.
 * Organic Technology: Everything the Aliens use.
 * Plunder: The Cult of Sirius are already your enemies. Raiding their buildings to take their stuff (and possibly, but not necessarily, kill some of them in process) won't make them more angry, and can only make them less rich - and therefore less capable of backstabbing you later. This gives some hands-on training, some equipment (plasma pistols and mini launchers) earlier than it hits open market, and you can sell expensive stuff (Psiclone $4500/+3, M4000 and High Explosive 800/2, Auto Cannon $1200/+3) to finance your early upgrades, and. However, capturing most equipment gives score, and victory (all enemies are dead, unconscious or have fled) gives you more score and aliens become tougher, thus it's a good idea to grab the good stuff and ammo (score +0 except plasma pods and missiles) and run.
 * It's possible to exploit game mechanics in "stun raids" on neutral organizations to steal their stuff - they won't shoot you if you won't shoot them with anything but stun grapple.
 * Point Defenseless: Laser Defense Arrays. The Plasma version is better.
 * Puppeteer Parasite: The Micronoids.
 * Raygun Gothic: The general art-style.
 * Real Time with Pause: One of two Battlescape modes.
 * Screw the Rules, I Have Money: You can do this. No, really. Even if every corporation in the city turns against you (either by subversion by the aliens or by hating you for any number of reasons) and the Senate ceases funding and threatens to shut you down, you can keep Fighting for Survival so long as your bank account remains in the positive... and as long as you have a functional base and a steady source of income to sustain your private army, you can go renegade. Want to show the Senate what you think of their threats? Go level half the city. Mwhahahahahahaha!
 * Sources of said income include: Raiding enemy corporations. Manufacturing and selling alien equipment. Selling captured alien equipment. Acting as a pusher for alien techno-drugs.
 * It is strongly recommended that you cease employing conventional vehicles as soon as feasibly possible, as alien-derived craft do not require maintenance fees or fuel. Doing so can considerably reduce your maintenance bills.
 * You cannot make an enemy of Transtellar, however, as they control all public transit. Civilians like your scientists and engineers require public transports to move from base to base, or to bring new hires to your labs. They cannot use your own vehicles for this, which means you can flip off the police, vaporise the assets of the Megacorps and violently depose the government but God help you if you annoy the Taxi drivers.
 * Another reason for not making enemies out of everyone is that you'll be tormented with frequent base invasions if you annoy someone too much. This invariably results in the death of a few of your unarmed and unarmoured scientists, as well as being extremely irritating.
 * What this boils down to is: Keep manufacturing equipment with the best profitability margins with your engineers for cash flow; keep raiding companies you don't like for equipment, while making your troops dualwield Devastator cannons and sweeping fire across their maps in real-time combat to make them so poor they cannot afford to raid you.. and keep bribing Transtellar to keep their opinion of you maxed out. You can theoretically level the entire city except for Transtellar.. including the government and the police.
 * The Syndicate: Three of them.
 * Teleporters and Transporters: Personal teleporters in Apocalypse.
 * Tube Travel: The Main form of pedestrian travel in Mega-Primus.
 * Urban Warfare
 * Uterine Replicator: Making babies the old-fashioned way is unpopular by the time of 2084, where they are now grown in Procreation Parks.
 * The Very Definitely Final Dungeon: The alien dimension is an excessively long version of this trope.
 * What Measure Is a Non-Human?: S.E.L.F. and the Mutant Alliance are groups protecting the rights of robotic and alien-hybrid folk respectively. And they help to fill X-COM's needs for soldiers with unusual abilities.
 * We Sell Everything: Subverted, as it required you to maintain good relations with a variety of Mega Corps to obtain troops, aircraft, weapons, safety from police interference, etc.
 * Strangely, We Buy Anything is not similarly averted. However, apparently Adam Smith Hates X-COM's Guts, since market prices for player-manufactured items in Apocalypse can only go down.
 * It should be noted that although We Buy Anything is in effect, you should never sell your Entropy Guns. Seriously, don't do it. At that point in the game, some corporations will have been taken over by the aliens and you'll have effectively given the enemy access to their Infinity+1 Sword.
 * Actually, Entropy Guns are completely useless against anyone with a working disruptor shield.. which your troops should be carrying three each by the time you start selling Entropy Guns. Unless you swap one of them out for the Cloaking Shield (when you get it) of course, which is recommended.
 * Weird Trade Union: The various organizations supply their respective goods and personnel to X-COM. Fail to protect them from aliens or just piss them off, and they will stop making business with you.

Interceptor

 * Apocalypse How: Class 6 and Class X-2: If you fail, the alien superweapon utterly obliterates Earth, leaving a smoldering husk behind. You get to turn the tables on them, though,  for an X-2. Technically, you can do it as much as you want, which is a little frightening.
 * Doomsday Device: The Aliens' Project Doomsday and our own Nova Bombs.
 * The Final Frontier
 * Gone Horribly Right: The cutscene when you complete research on the Nova Bomb, which of course includes a test. The pilot who reports that the test was successful doesn't sound too happy about it. But the player's avatar is.
 * Interquel: Set between TFTD and Apocalypse.
 * My Brain Is Big: The Psilords are apparently all brain.
 * Space Pirates
 * Space Station
 * Star-Killing: The Nova bombs in Interceptor.
 * The Very Definitely Final Dungeon: The Star system housing the Doomsday project, hidden

Enforcer

 * All Deserts Have Cacti
 * And Your Reward Is Clothes: Each difficulty level you beat Enforcer at in single play unlocks a few new skins for the titular robot.
 * Attack Drone: The Enforcer itself, and it can get one for itself.
 * Gaiden Game: Set during the First Alien War.
 * Stop Helping Me!: The scientist in Enforcer will leave you with a pathological need to kill him. Sadly, even at the beginning when you can actually see and shoot him, it has no effect. The Aliens get to him on Medium and Hard difficulties, in the end, but this lacks some satisfaction.

XCOM Reboot

 * Alternate Reality Game: Project: Enemy Unknown, also known as "InfiniVac", was started up in 2010 to help draw interest towards the XCOM reboot prior to its official announcement. It was placed on hiatus when 2K began retooling the game, thus delaying its release. Recently, as an attempt to draw much-needed attention to XCOM through a different approach (i.e., average citizens keeping tabs on strange phenomena instead of The Government doing so via the now-defunct InfiniVac Network), 2K started a new ARG called Citizen Skywatch. While news sites and online commentators alike were mostly speculating that the ARG was connected to either GTA 5, Bioshock, or an upcoming game called Agent, despite the heavy implication of UFO-related happenings from the title alone, an explicit link to XCOM was made by the appearance of a Citizen Skywatch section in the XCOM-specific part of 2K's official forums.
 * Blob Monster: The black goo.
 * Code Emergency: The InfiniVac Network from Project: Enemy Unknown was on "Code Black Lockdown" for quite some time.
 * Daylight Horror
 * Deliberate Values Dissonance: One of your recruiters is a black man, natural during this time period, most of your white american teammates have an issue about that. Likewise, one of the missions involves recruiting a scientist to XCOM who's had his professional career ruined because he's gay.
 * Development Hell: Delayed to Fiscal 2013(April 2012-March 31st 2013) as most of the dev team have been reassigned to help with BioShock Infinite.
 * Dolled-Up Installment: Pretty much confirmed by the developers.
 * Enemy Mine: Most of your team may not like each other due to very different issues (race, political beliefs, social classes, etc), yet most of them are willing to work together to stop the aliens.
 * Fan Nickname: Amongst other things, fans of the old games are calling 2K's misuse of the IP "contribution" Xenoshock. It's easier to get your mouth around than Yahtzee Croshaw's suggestion: Custard Pie Fights With Christopher Walken.
 * Genre Shift: To the FPS.
 * Grand Theft Me: The aliens have this ability.
 * Internet Backlash: The official forums for 2K's new "reimagining" are largely filled with fans of the original X-Com series who are hostile to the new game. The rest of the Internet doesn't seem to be much more kindly disposed, including comment threads on review articles and especially commentary at forums like RPG Codex. When the E3 2011 trailer came up, its "like/dislike" meter swiftly shot to being 70% dislikes, and it is currently hovering steadily at that point, with most of the comments on the video being negatively-flavored.
 * And now, the inevitable petition to get the game renamed.
 * In Name Only: Going by the details revealed in OXM magazine and and the first trailer, the new game looked like it was going to fit this trope in the manner of a Dolled-Up Installment. This was essentially confirmed when an interview with the developers revealed that the game is the result of 2K taking an independent project they had been working on for some time and adding the"XCOM" name when they remembered they owned the franchise. After all is said and done, the "reboot" looks well on the way to becoming this. The most you can say it has in common with the original series is that there's an alien invasion in there somewhere - certainly nothing much stands out as being something which other FPS games haven't had before - with the rest of the gameplay (right down to the camera-based research mechanic) having more in common with BioShock (series). Canon-wise, everything except for the names "XCOM" and "Elerium" has been dumped, and even those two words don't refer to quite the same things any more (A 1950's/60's FBI division as opposed to a multinational initiative that canonically originated in the 1990's, and what might be some sort of computronium or undifferentiated alien nanotech instead of a transuranic element). Fans were hoping for a comic-book "reboot"-style rebuilding of the original mythos, but such hopes were dashed after extensive interviews revealed the developers wanted nothing to do with the majority of the original IP, even going so far as to refer disparagingly to the original game as "kitschy". In greater detail:
 * Game mechanics are largely FPS based, taking most of their inspiration from BioShock (series) and Mass Effect, including "Sci Fi abilities" and points-based research (one of the few hard-ish nods to the original game, albeit hardly unique - once again see the Mass Effect games and even StarCraft 2 - and in the form of the a "points for loot" system, as well as possibly still a Bioshock-style "research camera" idea adapted to the new game, rather than the resource-juggling management sub-game of the original imported wholesale and tweaked to fit). The game may feature a team of scientists at this stage in development, but it would seem they are handed to you as the plot demands.
 * Manufacturing now appears to consist of feeding captured elerium into one end of a device discovered by the main character and picking up whatever you need at the other end, rather than the engineers and aforementioned management of the originals.
 * The era the game is set in is, as of the latest information, the 1960's, rather than the late 1990's/early 2000's of the original game (the near future, when it was originally released).
 * The game world is limited to North America rather than being global in scope.
 * Resources are now limited to Good Will/Funding, Elerium and Research, with only Elerium figuring into manufacturing (and also into purchasing/unlocking powers for your agents, apparently). Each is the subject of a single mission goal-type which can be found on the map of America.
 * There is no interception mechanic - indeed, UFO's seem to have been cut wholesale, unless one counts the relatively tiny (compared to an X-Com 1 battleship) Titan, though that seems closer in intent to a Cyberdisc, one of the alien heavy weapons units from the first game. Ironic for a series extended from a game that was originally named "UFO".
 * All missions are effectively terror missions - no more crash sites or landing zones (due to the loss of the interception mechanic). Players will play until the rising tide of aliens makes it either impossible or too risky to progress any further in the level (progess being usually being measured by how much elerium or research one has obtained), as opposed to the original games, where the goal was to eradicate the alien presence, with the only exception possibly being the "hold the line" mission type. Media suggests that the overall play time will be limited by how many towns are on the game map, as it would seem one more is lost to the aliens with each mission.
 * There have been some mentions of base management in the reboot - possibly, at least part of the strategic game will be similar. However, since the team is no longer multinational, instead being under the FBI there probably wouldn't be bases all around the world. Maybe not even multiple bases at all. Indeed, the existence of only one base seems to have been confirmed in a recent update of the official website, which words things as though there is only one. It also seems unlikely, due to the nature of the engine, that you will be able to alter the base in question, at least beyond unlocking pre-positioned rooms.
 * Missions appear on the main map in timed and sequential order - there is no longer any semi-random global AI managing the alien side of things and sending UFOs out to harass the world and the human player. Unlike the original games, tactical-game levels appear to be the same every play through, albeit with some level of randomised enemy and collectable placement.
 * Mention has been made in recent material of a tactical overview labeled "the Battlescape", which appears to be a case of the developers adopting an idea frequently floated on the game's official forums, though most fans feel the implementation leaves something to be desired - rather than a complete X-Com style tactical overview, it merely tilts your view to a third person viewpoint, and allows you access to Mass-Effect-style powers fueled by regenerable points named "TUs" via a Mass-Effect-style interface. On the other hand, the FPS portion of the game still seems limited to a scramble for research/elerium conducted alongside two or three FBI agents (as opposed to the eradication missions conducted by a possible 20+ trained soldiers in the original) mentioned above.
 * There is a main character (who, for some odd reason, is both the ultra-important leader of the fieldwork department and its lead headfirst-into-danger field agent), from whose first-person perspective the game is played, as opposed to the non-specific football-manager style focus on randomly generated soldiers of the original games.
 * A more recent trailer is a mixed blessing - on the one hand it shows (unfamiliar) humanoid enemies, which is a step closer to the original games, though not as large a step as many players had been hoping ("Where are the Sectoids?" is fast approaching meme-status amongst the long-time fans of the series). On the other, it would seem the cover-based gameplay shown reminds many of the commenters more of Call of Duty, and the graphics of Crysis1/2.
 * There has been no mention of morale mechanics, which were a pretty constant part of the ground combat-oriented games in the series.
 * There has been no confirmation on the presence of that staple of the series, the UFOpaedia database, though much of the hype has revolved around the claim that the developers have used new aliens because the original lineup were already "known".
 * Lost Forever: Choosing one mission over another may cause it to vanish forever.
 * No True Scotsman: Fans who don't like what they've seen of the reboot are likely to accuse fans who do like what they've seen of not being "true X-Com fans".
 * Revival: Not one that most of the old-time fans want, though.
 * Shout-Out: The game turns X-COM into a division of the FBI. Hmm, an FBI agent investigating the Alien Invasion of Earth... now why does that sound familiar?
 * Sinister Geometry
 * The Sixties
 * Starfish Aliens: This was one of the central design decisions of the reboot. The team stated that they wanted to create enemies so alien that it was completely impossible to predict their behavior on first encounter. Because of the fan-backlash, this was mostly ditched in favor of humanoid aliens, which itself got a backlash for not bringing back the classic aliens.
 * Super-Hero Origin: According to Word of God, the reboot tells the tale of how the organization started, and later became the worldwide organization it would become... after loosing all of the fantastic technologies discovered in the game.
 * Viral Marketing: The Citizen Skywatch ARG. Time will tell how well it works, and so far it has few participants, but those people seem to be enjoying it, and there are reports of fan-made posters appearing in certain towns.

XCOM: Enemy Unknown (2012)

 * Alternate Continuity/Continuity Reboot: Separate from the classic games, and despite speculation, canonically unconnected to the 2K Marin game.
 * Altum Videtur: XCOM's motto, Vigilo, Confido.
 * Apocalyptic Log: Do poorly, and the Situation Room feed will eventually end up looking like this, as panic and chaos spreads around the world from the aliens.
 * Arm Pistol: The new plasma pistol uses this form factor.
 * Ascended Meme: At E3 2012 the producers told Angry Joe there would be an achievement in honor of Spoony's infamous "BETRAYAL!" moment.
 * Attack Drone: You get your own in the form of the SHIV-with a whole tree dedicated to them.
 * Badass Normal: Any unmodified XCOM soldier who's survived combat against the aliens counts as this by default, especially once they start being equipped with advanced armor and weapons. Shaojie Zhang, a Council contact and former Triad takes it further, shooting a Sectoid in the head with a normal handgun in his introduction scene.
 * Badass Abnormal: Any XCOM personnel who's found to be "gifted" with psionic abilities, the most notable being French survivor-turned-recruit Annette Durand. By Enemy Within, this is extended to those given genetic modifications or converted into MECs.
 * Beam Spam: You get the option for this with with the Scatter Laser, Laser LMG analog and Laser SHIV.
 * The Berserker: Mutons, with their new Blood Call ability.
 * PAX East 2012 revealed a new enemy actually titled the Berserker, who has the ability to ram through the environment to get to your soldiers.
 * Blatant Lies: Sometimes, the lengths gone to keep XCOM a secret, covert affair border on this. Especially as more people notice mysterious military squads taking on aliens in the Situation Room's newsfeed.
 * Black Market: XCOM can sell some of its arsenal, recovered alien corpses and stock of alien technologies to interested Council member countries for a price. There is thus greater incentive to keep said technologies in one piece rather than just destroying them outright.
 * Blue and Orange Morality:
 * Body Horror: In addition to the Chryssalids themselves, there are the also the zombies that they create from people killed by them. If said zombies aren't killed quickly, their bodies burst and morph into new Chryssalids.
 * Broken Masquerade: Eventually, it becomes nigh impossible for the Council or XCOM to fully cover-up the aliens. But if you let global panic grow too far, the more chaos and societal breakdown spreads, making various countries more likely to view surrendering to the aliens as a viable option.
 * Call Back: The E3 2012 trailer shows a bald man wearing a suit sitting in the shadows.
 * The pre-order bonus includes a blonde dude with a humongous flat-top.
 * The shooting range in XCOM HQ is shown to use alien sprites from previous X-COM games as target markers.
 * The Chains of Commanding: You, as the Commander, have to bear the burden of not only leading humanity's first - and last - line of defence against the aliens, but also the lives of the personnel under your watch. Bradford as well feels the weight that comes with sending soldiers off into almost certain death.
 * Character Customization: You can customize the visual appearance of the soldiers.
 * Chest Burster: Chryssalids make a return, and are even more dangerous than ever.
 * Continuity Nod: Dr. Vahlen's notes mention her coming across heavily redacted references to Elerium from the 1960s, a nod to The Bureau: XCOM Declassified.
 * Cybernetics Eat Your Soul: Dr. Shen, XCOM's chief engineer, suspects that the Floaters are suffering this. In addition, he wonders whether incorporating the aliens' cybernetic technology on humans would consume them all.
 * The Floaters, a partially-robotic alien type derived from Mutons, are suspected by Dr. Vahlen to have been turned that way against their will.
 * Development Gag: The logo appears to be de-hyphened, much like the FPS. But then you look at the negative space in the last three letters...
 * Do Not Go Gentle: In some countries with high panic or otherwise on the verge of pulling out from XCOM, it's mentioned that some politicians, militia and other national factions won't go down without fighting against the aliens, however futile it may be.
 * Dueling Games: With Xenonauts, although Jake Solomon is cordial about the competition.
 * Elaborate Underground Base: Instead of the classic top-down view flat base, this game uses a side-view multi-level base. One of the changes announced at PAX East 2012 is that this will be the player's only base.
 * Elite Mook: Late-game, expect to encounter Armored Floaters and Elite Mutons, the latter being a sort of guard to the Ethereals.
 * Evil Counterpart: Mutons have been described like this, an alien SEAL Team Six to fight your own troops.
 * Featureless Protagonist: Although the original games did technically have the player in the role of the one running operations, Enemy Unknown marks a point wherein it's further emphasized that you are the Commander.
 * For Science!: Dr. Vahlen revels in not only getting her hands on alien tech but also getting her hands dirty with "interrogating" aliens.
 * Game Mod: The most (in)famous being the Long War mod, which makes several changes while taking the game's already hard difficulty Up to Eleven.
 * Godzilla Threshold: XCOM in general, and the considerable amount of leeway the Council's willing to give regarding collateral damage, amount to this.
 * Gender Is No Object: XCOM has its fair share of female operatives who can be just as capable as the male ones. Given that said operatives hail from what are supposed to be the best of the best from various countries, not to mention XCOM needing every capable soldier on hand in light of the alien attacks, it's justified.
 * Herr Doktor: Dr. Vahlen, who's as German and ethically dubious (if well-meaning) as they come.
 * The Greys: By way of the Dover Demon, by the looks of things.
 * Harder Than Hard / Idiosyncratic Difficulty Levels: The hardest difficulty level is called "Classic". Enemy Within meanwhile introduces "Impossible."
 * There is also another method of play called "Ironman," where the game will only have one save file for that playthrough, and will save for the player after every turn during combat, meaning if you make a mistake, there is no reloading to before it happened. Now try that on Classic difficulty...
 * Jack Bauer Interrogation Technique: Played with. Dr. Vahlen conceives a way to "interrogate" captured aliens for research or vital information that ultimately amounts to a For Science! version of this trope.
 * Jet Pack: Your troops get these during the late game. The new Floater has one... built in.
 * Lensman Arms Race: Like in the original XCOM games. Further lampshaded by Dr. Vahlen's comments on how research into the aliens is accelerating scientific and technological development by centuries over the course of just months.
 * The Men in Black: The Thin Men, inspired by the Slender Man, and likely the inspiration for him in-universe. They're humanoid infiltrators with extreme agility and the ability to vomit acidic gunk in close combat.
 * Mecha: The aliens have their share of mechanized adversaries. But the largest and most lethal of them would be the Sectopod, a large robotic weapons platform that can wipe out whole squads if unprepared.
 * Mind Rape: The Sectoids seem to also have the full range of fun little Tricks from the original as well as likely even more.
 * Mission Control: Represented in-game by XCOM's second-in-command, Bradford, who also answers to the Council.
 * Multinational Team: Soldiers under XCOM hail primarily from Council member countries, though there are exceptions.
 * Next Sunday AD: Like the original X-COM: UFO Defense. In this case, the game's set around 2015.
 * Nintendo Hard: The higher difficulties can be just as punishing as in the original XCOM titles. Even more so with the Ironman and Second Wave options on.
 * No Mouth: The Sectoids.
 * No Such Agency: As XCOM's a covert programme that answers to the Council, it's not formally recognized. As a result, even high-ranking officials not in the know are surprised by the appearance of an "unknown" military outfit taking the fight to the aliens.
 * Not So Above It All: For all the aliens' sense of superiority and arrogance, capturing them alive for "interrogation" with Dr. Vahlen reveals that they too feel fear . The only real exception are the Thin Men, who simply stare down its interrogators and instead Face Death with Dignity.
 * Nothing Is the Same Anymore: It's brought up that even if XCOM wins, it would still mark an end of an era for mankind. With all the knowledge, technologies and enhancements being discovered, nothing would ever really go back to what they were before the aliens arrived.
 * Omniscient Council of Vagueness: The Council, a collective of 16 powerful countries (represented in-game by a single spokesman) that oversees and funds XCOM, all the while keeping the full extent of the alien invasion hidden from the public. And they're the good guys.
 * One Man Army: While a single alien or two can easily wipe out even a well-equipped squad if you're not careful, it's still possible for a single XCOM soldier to turn the tide of battle.
 * Powered Armor: Eventually, XCOM can research armor that ultimately amount to this. On the aliens' side, there are the Mutons and their derivatives as well as the Mechtoid, an armored non-psionic variant of the Sectoid.
 * Pretentious Latin Motto: Vigilo, Confido, or "watch, I am confident" is seen on the chestplate of XCOM armor in the E3 trailer.
 * Psychic Link: Sectoids can use their telepathic abilities to boost the stats of their allies.
 * Running the Asylum: A meta example. The developers are all fans of the original games given a shot at their own take on the series. Despite concerns that the resulting product would suffer as a result, it worked.
 * Shout-Out: To Gerry Anderson's UFO TV show (which largely inspired the original X-COM): while the player is at HQ, Bradford may make a comment about picking up a transmission from "somebody calling himself Ed Straker going on about 'shadow operatives'."
 * Spy Satellites: Used to search for UFOs outside of your main base's radar coverage. They also serve as reassurances to Council nations under their coverage, giving XCOM additional funding and bonuses in the process.
 * Transforming Mecha: The Cyberdiscs can transform between a nigh-invulnerable but unarmed disc form and a vulnerable but heavily-armed spider-bot form.
 * Uncanny Valley: The Thin Men, who can almost pass themselves off as human at first glance if not for their slender frame, reptilian eyes and unnaturally fluid motions.
 * The Worf Effect: The tutorial mission has your XCOM squad finding out that a small group of Sectoids managed to wipe out a German GSG force sent in previously to investigate, just to highlight how much of a threat the aliens pose to human militaries unprepared to face them.

XCOM: Enemy Within (2013)

 * Ancient Conspiracy: It's implied that EXALT has been a going concern for a long time.
 * Bio Augmentation: Enemy Within makes it possible to genetically modify your soldiers with various enhancements.
 * Cyborg: It's possible as well to use Meld to turn soldiers into MEC troopers. Who are essentially cyborgs who can interface with heavily armored battle suits.
 * Everyone Has Standards: Dr. Vahlen, for all her obsessions with SCIENCE, balks at the excessive lengths EXALT go to genetically augment its agents.
 * Foil: EXALT, which serve as this to both the Council (being a secretive organization seeking to Take Over the World) and XCOM (given how it intends to use the aliens' technologies and abilities for their own ends).
 * Gratuitous Foreign Language: Foreign language voice tracks are introduced to further emphasize the Multinational Team aspect of XCOM, such as French, German, Polish and Russian.
 * He Who Fights Monsters: A recurring concern from both Dr. Vahlen and Dr. Shen is whether the various enhancements that could be done on XCOM personnel are ultimately for the betterment of mankind or slowly removing their humanity, ultimately becoming little better than the aliens they're waging war against.
 * Hidden in Plain Sight: EXALT's shtick, often operating under the nose of both XCOM and the Council.
 * Mecha: MEC Suits are not suits, unless the pilots have legs amputated or broken and implanted with extra 2-3 joints.
 * Sharp-Dressed Man: EXALT agents to a man dress in spiffy business suits akin to the 1960s Bureau in contrast to XCOM soldiers.
 * Take That: The general aesthetic of EXALT seems to be this to The Bureau: XCOM Declassified.

XCOM: Long War

 * Anyone Can Die: The mod makes a point to emphasize that yes, no one is safe.
 * Approval of God: Jake Solomon has described EU/EW as "a twenty-hour tutorial for Long War." Many of the features of XCOM 2 were inspired by it.
 * Ascended Meme: Players get Gen. Van Doorn as a playable character after succeeding at the mission to rescue him.
 * Game Mod: A big one!
 * Nintendo Hard: Even the easiest difficulty can be a challenge compared to the hardest settings on "vanilla". It's not that the aliens have ridiculous amounts of health or aim; rather, the whole game itself is extended -- soldiers are fatigued for several days after a mission even if they're uninjured (and soldiers that are gravely wounded can be out of action for over a month), items that could be built instantly in vanilla require more resources and time to be constructed in Long War, and research times are greatly extended.  (That being said, the game's not unfair -- the aliens have their own research and supply limitations, panic takes longer to build up, and lost countries can be recaptured.)

The Bureau: XCOM Declassified (2013)

 * Deliberate Values Dissonance: Given that it's set in the 1960s and during the Cold War, it's very much in effect. To the point that even the Bureau's HQ seems rife with cigarette smoke.
 * Genre Shift: Compared to other games in the franchise, it's a third person shooter with squad mechanics and a strategic layer meant to be reminiscent of other XCOM titles.
 * No Such Agency: A more literal example compared to Enemy Unknown. As in this continuity, XCOM starts out as a secret US Government Bureau whose existence is known only to the President and some high-ranking officials.
 * Origin Story: Similarly to the original XCOM Reboot, the game depicts the early days of XCOM. In this case, as a secret US government agency meant to hunt down Soviet infiltrators retooled to fight alien invaders.
 * The Sixties: The game itself takes place in 1962.
 * Spiritual Successor: To the original XCOM Reboot concept.
 * Zeerust: Deliberately invoked. While the game starts off with conventional Cold War-era firearms, eventually you and your squadmates gain access to bulky reverse-engineered variants of the aliens' weapons that wouldn't be too out of place in a period Sci Fi movie.

XCOM 2 (2016)

 * Airborne Aircraft Carrier: The Avenger, XCOM's new and mobile base of operations. Though technically, it's an old alien supply vessel from the events of Enemy Unknown/Within that's been heavily modified.
 * And I Must Scream: It's strongly implied that the Commander has been heavily experimented on by ADVENT and the aliens.
 * Ascended Meme: The developers has since recognized the appeal of the Viper, affectionately known among some fans as "Snek."
 * Bad Future: The whole game takes place in one, being based on the game over scenario in Enemy Unknown/Within.
 * Character Customization: Even more so than in Enemy Unknown. Characters can get customized appearances, such as their faces, uniforms and tattoos. In addition, they can change backstories, genders and nationalities mid-game.
 * Crap Saccharine World: The united ADVENT-run world is on the surface rather pleasant and utopian...so long as you keep in line, stay in the refurnished cities and are otherwise not a target for the aliens' myriad abductions.
 * Crapsack World: Away from ADVENT's (direct) gaze, survivors, refugees and Resistance militia struggle to make a living. This isn't helped at all by the Blacksites and various nasty activities ADVENT and its alien masters have been up to, all of which are kept hidden away from the public eye.
 * Defector From Decadence: Dr. Richard Tygan, XCOM's new chief scientist, used to work for the ADVENT administration until he began to realize what they were really doing.
 * Drowning My Sorrows: Bradford, who makes a return as XCOM's Mission Control, is mentioned as having become a depressed alcoholic over the years as he hid from the aliens. At least, until he answered the call and helped revive XCOM.
 * Ensemble Darkhorse: The Viper. Once she entered the gameplay trailer, players were smitten.
 * Expy: In addition to having some similarities with the Cult of Sirius from X-COM Apocalypse, ADVENT also functions as a considerably more powerful version of the Combine from Half Life 2, and with better PR. Especially given how it's trying to (on the surface) encourage everyone into the refurnished cities.
 * Faceless Mooks: ADVENT's soldiers and its higher-ups, who seem purely human at a glance. Justified in that their concealing helmets are meant to disguise their various enhancements and alien modifications from the public.
 * Featureless Protagonist: Downplayed, but you're still playing the same Commander from XCOM: EU/EW, with whatever backstory you've come up for said Commander.
 * For Science!: Dr. Tygan doesn't particularly approve of Dr. Vahlen's more brute methods. But even he admits that there's a thrill in working under the tense conditions XCOM tends to operate under.
 * Game Mod: The game is stated to be very moddable, with a number of mods already in development and some expected to come out the day of release thanks to the toolkit made readily available.
 * Generation Xerox: Dr. Chen's daughter serves as XCOM's new chief engineer.
 * Glamour Failure: The Thin Men are still around, and much more human in their looks and actions for the sake of PR. On the other hand, their reptilian skin is still visible and they still have to don sunglasses. But by the time XCOM 2 takes place, it's not as big of a concern given that the aliens had already won.
 * It's speculated by Dr. Tygan that the more visible manifestations of the alien enhancements in ADVENT soldiers aren't intentional, but get around that by covering their faces in cleverly-designed armor.
 * Glory Days: Bits and pieces of memorabilia from the old HQ, including a tattered original XCOM flag are onboard the Avenger, and treated with due reverence.
 * Gratuitous Foreign Language: Expounded upon from Enemy Within. Not only are there more foreign language voices corresponding to their respective nationalities, but there's more variety in English dialects as well.
 * Humanoid Abomination: The Faceless, a new alien type that can disguise itself as any regular civilian. Its true form, however is a tall monstrosity that looks straight out of Amnesia and The Thing.
 * La Resistance: In addition to XCOM itself, there are the various Resistance groups fighting the aliens. Getting the Resistance's support (and spreading the uprising against ADVENT) is thus valuable to XCOM.
 * Legendary in the Sequel: By the time XCOM 2 takes place, the Commander has become a legendary, almost mythic figure.
 * Les Collaborateurs: ADVENT in general. Its soldiers are also mentioned as having been given enhancements by the aliens, the higher-ups being increasingly alien.
 * Multinational Team: Further highlighted this time around, especially given how XCOM members still display their heritage and even their national flags in defiance to ADVENT.
 * My Greatest Second Chance: Despite having failed to stop the Alien Invasion, XCOM and the Resistance still think highly of the Commander. And this time, you might be able to stop the alien threat once and for all.
 * Omniscient Council of Vagueness: The Council, or what's left of it, has long since succumbed to ADVENT. There are still those on the inside however who are trying to support the Resistance. The Informant in particular, previously the Council's spokesman, serves as XCOM's main contact to what's going on within ADVENT.
 * One World Order/Vichy Earth: ADVENT, which has "unified" the world and rules it on behalf of its alien masters.
 * Race Against the Clock: Taking too long, doing too poorly or otherwise failing to stop enemy operations would allow ADVENT and its alien masters to complete a mysterious programme called the "Avatar Project."
 * Ruins of the Modern Age: The decaying remains of modern-day buildings, facilities and whole settlements still litter areas that ADVENT had largely abandoned to the elements and its blacksite operations. In-game lore suggests that there are still some people struggling to hide in such ruins away from ADVENT and the aliens.
 * Spiritual Successor: Of sorts to X-COM Apocalypse, given the similar premise.
 * Starfish Language: ADVENT soldiers all speak in an alien language, to further highlight their status as Les Collaborateurs and how they're becoming more like their alien masters.
 * Time Skip: The game starts off in 2035, decades after the aliens won.
 * Took a Level In Badass: Sectoids this time around are much more dangerous and human-like. While Sectopods, already a powerful threat in EU/EW, have gotten even more overpowered.
 * Villain with Good Publicity: ADVENT and its alien masters are doing their best to win over humanity and promising utopia while masking the dark truth behind it all. XCOM and the Resistance's actions however can break their PR over the course of the game.
 * Utopia Justifies The Means: Enough that ADVENT and its masters will do anything to make sure the "Avatar Project" is completed.
 * What Happened to the Mouse?: Dr. Vahlen's fate is still up in the air. All that's known is that she went missing after the aliens won. Averted however with Dr. Shen, who died trying to secure the future of XCOM sometime before the events of the game itself.
 * You Can't Thwart Stage One: The canon ending of EU/EW is that the aliens won.
 * Your Terrorists Are Our Freedom Fighters: XCOM's new function is to run around causing trouble for the alien government. Whether it's terrorism or fighting for freedom is a matter of interpretation.

Click End Turn button:

HIDDEN MOVEMENT

*pew* *blam* "Aughgghggurglegurgle..." *slither* *slither* *pit* *pat* *tap* *click-click* *BOOM* "Aiiieeegurgle gurgle..."