Killing Floor

""I told you, I am welding this doah!""

A cooperative online Zombie Apocalypse First-Person Shooter for PC published by Tripwire Interactive on the Unreal Engine 2. Originally a mod for Unreal Tournament 2004, in 2009 an official retail version was released. While generally an updated version of the mod, there are changes - notably the "perk" system, a series of six different "classes" that players can choose.

You and up to five friends take the roles of a squad of a bunch of surviving military, police personnel, street thugs, the Pyro, a Queen's Guard, and more sent into various areas to wipe out the zombies Specimens of a Freak Lab Accident Gone Horribly Wrong. Games are divided into several rounds, in which players must kill a required number of specimens. Between rounds, the players have a minute (or ninety seconds on Beginner difficulty) to visit the Trader, a woman who sells you weapons, armor, and ammo. After all the set rounds are completed, one last round against the Patriarch, the creator of all the specimens, who has become a genetic monstrosity himself, happens. The game's story is not exactly a masterpiece, but it has an obvious goal.

If the basic premise sounds like anything familiar, it's totally different. (Mainly because the original Killing Floor mod came out first.)


 * All There in the Manual: The entire plot, centering around a leading stem cell researcher, CEO, under-the-table-unorthodox-science-military-applications-expert, and doctor of bio-genetics and engineering named Kevin Clamely, whose research became less than practical after the murder of his son.
 * Alternate Reality Game: Is one of the 13 indie games that formed the bulk of the material of Valve's "PotatoFoolsDay" Portal 2 ARG.
 * AKA-47: Zig-zagged. There are things like the AA12, SCARMK17, MP5 and M4, and at the same time there's the "Hand Cannon", "Bullpup", and "Combat Shotgun". Also, similar to Left 4 Dead 2, the game's "AK47" is actually a Draco AK-pistol, modified with an unused AIMS-style folding stock.
 * Amusement Park of Doom: The summer Abusement Park map, complete with freakshow skins for the Zeds and Creepy Circus Music.
 * An Axe to Grind: One of the melee weapons is a fireaxe.
 * Arm Cannon: The Patriarch's preferred method of problem removal, and the primary weapon of the Husk.
 * And with the Twisted Christmas 2011 update, you can use the Husk's arm cannon as a weapon yourself!
 * Armor Is Useless: Gameplay and Story Segregation in the opposite sense - a few characters are wearing heavy gear/armor that does nothing useful (the description for Lee Baron specifically mentions that specimen claws and teeth tear right through his EOD gear), but in-game body armor is almost necessary to survive.
 * Artificial Brilliance: Specimens will actively move to avoid hand grenades. Husks aim their shots to impact the ground near their target, similar to a human player with a rocket launcher. And, in an example verging on Artificial Stupidity, specimens will sometimes jump for the hell of it, just to throw off a player's aim. And speaking of behavior that's situationally stupid, most of the specimens seem to avoid approaching players in a straight line if they're already part of a large group so they can flank better.
 * Artificial Stupidity: Pathing for the specimens can make them suddenly change their mind about what direction to run when chasing players. This has been abused to make the Patriarch attempt to run and heal by trying to blow up a welded door in the same room as the players unloading into him. Bonus points if the door he came through is still open.
 * Speaking of pathing, the floating light that leads players to the trader likes to spin around like a drunk instead of pointing players in the correct direction if they don't stop moving for a second to let it get its bearings.
 * In at least one level, the path may point towards the open windows in a building... which of course would cause players to fall to their death if they tried that.
 * Ascended Meme: One of the Circus Scrake's lines is "And not a single fuck was given that day".
 * Awesome Yet Practical:
 * To quote the Patriarch, "Everything is so simple when you have a rocket launcher for an arm!"
 * Thanks to patches, the L.A.W. (rocket launcher) again belongs here. Weight is slightly reduced, 50% increase in ammunition capacity, and greatly increased damage and explosion radius which can now be further amplified with the demolitions perk.
 * The SCAR rifle, which is endgame equipment for the Commando and deals damage comparable to the Lever Action Rifle per bullet.
 * George, otherwise known as "Herman the German" because of his meticulously kept WW 2 German uniform, wasn't planning on beating up mutants with his replica entrenchment spade- but it worked well enough.
 * Awesome but Impractical: The Berserker perk can turn into this in later waves or later difficulties - being up close and personal with that many enemies, in particular that many Fleshpouds and Sirens, gets you killed very quickly.
 * On the other hand, expert Berserker players can easily run circles around most zeds, and survive without any backup even on the highest difficulties.
 * Being able to stun many specimens with melee attacks definitely helps... unless your teammates interupt the effect with their firearms.
 * Going Guns Akimbo often has this effect, in that you have to sacrifice precise aiming for doubled firing rate and ammo capacity.
 * It does not get in the way, however, if you just keep them handy for close encounters. Bullet-spam, aiming or not, with dual pistols is a decent way to get you out of a jam.
 * The MP7M is this for anyone not playing as a field medic. It's decently powerful and allows you to heal teammates from much longer range, but if you're not playing as a medic, it only holds 20 rounds per magazine, burns through that extremely fast, and takes forever to recharge its healing dart. On top of that, Medics get a massive discount on the gun - for everybody else, it costs 3000 pounds.
 * The MP5M proves to be more practical. It fires more slowly, does almost twice as much damage, and holds 32 rounds (up to 64 if sufficiently leveled as a Medic), but if you are not a medic it costs you 5000 pounds. For reference, the AA 12 cost 4000 pounds, a M4 with grenade launcher will put you 3500 pounds in the hole, and all the other class-based super weapons (such as a six shot grenade launcher,) are priced at a flat 2500 pounds.
 * Many commandos find asking a medic for a hand me down medic gun to be a good tactic, since they can carry it with two assault rifles, a hand gun, body armor, and five hand grenades, plus ammo for the above.
 * The same goes for the MAC-10 if you're not a Firebug, which among other drawbacks, won't set enemies on fire.
 * Although it can Death of a Thousand Cuts very efficiently when used by a Commando due to the reload-speed bonus. Attempting this will net you plenty of criticism, however.
 * The Combat Shotgun, whose only advantage over the regular shotgun is semi-automatic fire useful for pinch-hitting incoming Scrakes and Fleshpounds. On the flipside, it deals the exact same damage as the regular shotgun, reloads at the same rate, can only hold six shells and costs five times as much.
 * Badass Normal:
 * Two of the default player characters are just part of the police force.
 * Foundry Worker Aldridge, who was rudely interrupted during his lunch break.
 * DJ Scully, an AWOL soldier turned DJ lured back to the battlefield.
 * Mr. Foster, a day trader who was working on an autobiography before the outbreak.
 * Dr. Gary Glover, a scientist involved in the project that ravaged London.
 * Mike Noble, who tapped into his homicidal side at a rave Gone Horribly Wrong.
 * Harold Hunt, the frontman for underground punk band "The Fecking Nancies".
 * Kerry Fitzpatrick, an Ax Crazy escaped convict being transferred to a psych ward.
 * Paramedic Alfred Anderson, who was working night shift at the time of the outbreak.
 * Chopper Harris, who was now free to beat on people with no consequences.
 * Kevo the Chav, who grew a pair in time for the apocalypse.
 * Reverend Alberts, who wasn't expecting to have to apply his knowledge of horror films.
 * Bill "Baddest Santa" Weeks, a Mall Santa who got fired and is taking it out on the specimens.
 * George and Nikolai, a couple of WW 2 War Reenactors.
 * Bad Santa: The Christmas-themed Bloats and Patriarch.
 * Beat Them At Their Own Game: Two achievements related to killing Husks with fire-based weapons. The newer one fits better because the weapon involved is the same one they're armed with.
 * There is also an achievement for killing two Scrakes with the chainsaw, their signature weapon, in one wave.
 * Berserk Button:
 * The Fleshpound does not appreciate being shot or people running from him. The Fleshpound also doesn't appreciate it when it can't reach its target. Blood will rain like mist as it rips apart anything around it in a frustrated fury should a player find a spot it can't reach. Makes it difficult to earn cash since the player does not get money for specimens the Fleshpound kills.
 * This is actually a great way to win a round if you team is likely to die: if one person can glitch to an unreachable spot (and take out any Husks that approach) the Fleshpounds will basically act as a Mole, leaving only a few Specimens left to deal with. In fact, the only specimen that can survive this tactic IS the Fleshpound.
 * Bored specimens will turn on each other.
 * The Berserker: The Berserker perk. With his brisk movement speed, absurdly thick skin and mighty swinging arm, he specializes in closing in on the Specimens and fighting at spitting distance, first with the humble knife or machete. Later, with some more dosh, he can keep up his nimble ways of dancing in and out of enemy range with renewed strength thanks to the fire axe, katana, or claymore, or become the world's most painful doorstop with a bloody awesome chainsaw.
 * Big Damn Heroes: Can happen to you, or anyone for that matter.
 * Blade Below the Shoulder: The Gorefast. The Scrake too, but with a chainsaw.
 * Body Armor as Hit Points: The Medic has this, as he gets 100% protection from damage to his health when he has a kevlar vest, in addition to more armor overall. Kevlar normally reduces damage to health by about 77%.
 * However, some types of damage bypass kevlar altogether.
 * Body Horror: The Summer Sideshow Gorefasts. Good Lord, how are they still alive with that many swords in them? And the Sideshow Crawlers, for those of you who like their Body Horror in the realm of medical possibility.
 * Boom! Headshot!: The Sharpshooter perk lives on this trope, but any bullet-shooting weapon can do it. Also of note: headshots on any specimen (except the Patriarch) will remove its special ability if they don't kill it outright, aswell as making them slower and eventually killing them due to bleeding.
 * Boring but Practical: The 9mm Tactical you spawn with, while weak, is still useful for beheading low-level specimens, and it's one of only three weapons equipped with a flashlight. And at higher Sharpshooter perk levels, it does increasingly respectable damage, nearing the point of becoming a viable primary weapon against all but the toughest enemies.
 * The Lever Action Rifle (commonly abbreviated as the LAR). While slow-firing, it has decent power and it's the second cheapest weapon in the game at 200 pounds, making it a good early-game sidearm.
 * The Knife, which you also spawn with, is nominally a last resort weapon. Equipping it allows you to run faster, however, plus no matter what perk you choose, a hard swing to the neck of a Clot or Gorefast is still going to kill them immediately.
 * Boss Banter: The Patriarch has a rather large list of lines. "Excellent, another batch of subjects!"
 * Breakout Character: For a game with an All There in the Manual plot, and characters that have no actual differences other than appearance and voice (there's a total of two voices among the 31 playable characters), DLC Mr. Foster seems to be slowly becoming the main character of the game.
 * British Accents: Taken to hilarious levels. Justified because it takes place in the U.K. and the "voice actors" are just the developers who themselves live in Britain for the most part.
 * British Royal Guards: Captain Sir Richard Wiggins, a minor aristocrat with a commission in the royal guards. He sees specimen hunting as jolly-good fun. His outfit consists of his roughed-up and missing-a-sleeve red coat and fuzzy hat, with some pouches and holsters tacked on.
 * Bullet Time: ZED time, which occurs randomly when a player does something impressive, e.g. getting several headshots, taking down a tough enemy or scoring a kill at an absurd distance. Time slows for a short time, and multiple slowdowns can be chained by the Berserker and the Commando.
 * Butt Monkey: Police Sergeant Davin is this, according to his background. He's been looking for a big change in his life. It's safe to say he got one. All hail the end of the world.
 * Calling Your Attacks: Played straight with the Patriarch, who utters distinct lines before his rocket or gatling gun attacks. Subverted when he turns invisible, charges, and without so much as a word punches a Combat Tentacle through your face.
 * Also done with the Fleshpound, which stops in place and screams angrily before charging at the players.
 * Not quite attacks, but player characters loudly announce everytime they reload or heal another character with the syringe. They also comment some of the higher tier weapons when they pull them out.
 * The Cameo: The RED and BLU Pyros from Team Fortress 2 appear as selectable character skins. See Crossover.
 * Chainsaw Good: Go ahead and guess what one of the best melee weapons is. It flits in and out of the number one spot, and is looking forward to some cool balance changes. The Scrake also has a chainsaw for an arm.
 * Christmas Elves: The Clots became goblin-like grotesqueries of this trope for the Christmas events.
 * Circus of Fear: The summer event's theme.
 * Color Coded for Your Convenience: The Fleshpound has a bizarre glowing... thing on his chest that Turns Red instead of yellow when he gets mad. Player characters use to all be green and blue, too.
 * That 'thing' in his chest is an adrenal pump, and when he gets pissed, it... Pumps adrenaline. Which leads to every player in-game yelling 'OH SHIT!' and running.
 * Combat Medic:
 * Even if you go Field Medic, you're going to spend a lot of time shooting at zombies, unless things start to go horribly wrong. In fact, the Medics are actually good in combat, since the Medic perk gives massive bonuses to your armor and ability to heal yourself, not just others.
 * The Scrake is meant to be the specimens' version of this. He's supposed to have been the ultimate field medic, able to take crazy amounts of punishment while saving the lives of other specimens (with amputations via chainsaw when necessary because why the hell not), but he only learns by being wounded himself and has taken an unusual fascination in dishing out and receiving pain.
 * Cool Guns: A large selection of such.
 * Cool Mask: A large number of the playable characters wear some kind of mask, mostly gas masks.
 * Crazy Survivalist: According to his bio, Sergeant Powers lost his entire family to the specimens. Oh, and he collects freak fingers. Apparently he disconcerts the rest of the characters.
 * Critical Existence Failure:
 * The medic has upgraded armor and can thus take heavy amounts of damage. Once he loses that armor he's as fragile as the rest of the team.
 * The actual spirit of this trope is averted by the player characters, who move a bit slower when their health is at about 40, and even slower when that's halved, which is also accompanied by the screen becoming near-totally blood-red.
 * The Specimens all play this straight if you don't take off their head.
 * Crossover:
 * For the Christmas event, anyone who owns both Killing Floor and Team Fortress 2 received a pair of Pyro player models for KF, and Mr. Foster's gas mask and tie for the Pyro in TF2.
 * Those who preordered The Ball received a player model of that game's protagonist Harchier Spebbington.
 * Killing Floor's involvement in the aforementionned Alternate Reality Game climaxed with the addition of KF-Aperture, a Portal-based map with things such as pressure buttons to open certain doors. When the ARG was still running, the Trader was temporarily replaced with what appears to be GLaDOS.


 * To a lesser extent, there's one with Red Orchestra 2 in the form of Nikolai and George, obtained by pre-ordering or purchasing the Digital Deluxe edition. Doing so also gave you a Stalhelm and a Pilotka to use in Team Fortress 2.
 * Cutscene Incompetence: Of a sort, when the Patriach first spawns there are about 10 seconds during which you can't control your character. If he spawns near you, the camera continues viewing the Patriarch from third-person, during which you can't do anything at all while he can do whatever the hell he wants to you.
 * Damage Discrimination: Fleshpounds do not play well with others, and don't appreciate other specimens being in the way of them and their target. Scrakes, meanwhile, don't enjoy being bitch-slapped out of the way. One plus one equals an enjoyable diversion. Other specimens are much more forgiving of inadvertent friendly fire, but do occasionally turn on their fellows.
 * Dead Baby Comedy: Pukey the Clown is a fan. "Why'd the dead baby cross the road?"
 * Deadly Doctor: Doctor Dave from the Steampunk DLC. He also has a Nice Hat (top hat, of course).
 * Deadly Lunge: The Scrake, the Gorefast and the Fleshpound all start rushing at you once they take enough damage or get close enough. The Crawler does a more literal lunge, attacking by leaping at your face.
 * Dead Weight: The Bloat is fat, but he's not really a zombie.
 * Deadpan Snarker: The player characters are quick to call out specimens on just how outrageous some of them look or act.
 * "A machine gun for an arm? No effin' way!" "He goes bloody invisible too?" "Rockets, too? Now he's really taking the piss." "Bloody hell, what's he got on his arms?" Are just a few gems.
 * Some of the other responses qualify aswell. Be it berating another character for not holding still while trying to heal them or one of the voiceclips for asking for money: "Where's my bloody benefits check?".
 * Defector From Decadence: The Lieutenant Masterson player-model is apparently one of the last specimens created, who escaped and brought the army to take out Horzine. Turns out this was exactly what the Patriarch had expected him to do.
 * Some characters from the character packs are apparently former Horzine employees - Dr. Gary Glover, a scientist in a hazmat suit, is one of the last survivors of the team directly involved in the creation of the Specimens.
 * Desperation Attack: A common tactic among doomed players is to throw all one's grenades at your feet when surrounded to kill as many zeds with you as possible.
 * Can also be done unintentionally, as grenades, pipebombs and other explosives can easily kill the user (and in case of the pipebombs, those can go off if the user steps on them).
 * Difficulty Spike: Likely to compensate for fewer achievements than other holiday-themed events, most of the ones for the 2011 Halloween update specifically required the player(s) to play on Hard mode or above.
 * Ding Dong the Witch Is Dead: It is possible to kill the Patriarch while there are other specimens alive, in which case they just stop moving while the YOUR SQUAD SURVIVED text is displayed.
 * What's more, any dead player respawns at this point as usual after a round ended.
 * Disaster Dominoes: DLC character Lance-Corporal Lee Baron was already in full EOD gear dealing with a bomb threat in downtown London when the Specimen attacks began. He learned that the best way to keep them at a distance was to blow them up.
 * Disc One Nuke: A maxed out perk lets the player start the game with certain weapons, including (but not limited to) a chainsaw, a flamethrower, or a crossbow. Some perks also spawn with body armor at the highest levels, not to mention the massive discounts for perk-specific weapons.
 * Sometimes players may also find random low-to-mid tier weapons lying around. Depending on your perk, an early bullpup or fireaxe might be all you need for the first 7 rounds or so when you can afford the big ones. Or if you play a perk that can carry a lot, this can be used to make a lot of dosh at the trader early on.
 * Double Entendre: Anything said by the Trader could - and is intended to be - taken as one.
 * In the Abusement Park, there's machines hawking "Rainblow" condoms.
 * Circus Clots will occasionally say "Just let me stick the tip in"
 * Drop-Dead Gorgeous: Okay, she's not dead, per se, but the developers (or alternately, Kevin Clamely himself) are apparently a bit too fond of the Stalker. Let's see: she's nearly naked, it's apparent her breasts use jiggle physics when she dies in Zed Time, and the two events where they've reskinned the Zed, she was a Santa Babe (referred to as Mrs. Claws, naturally) and The Lovely Assistant, respectively. And both reskins were blonde.
 * Dynamic Difficulty: Specimens grow in numbers as more players join. Most specimens also gain more health depending on the number of living players (particularly the Fleshpound and the Patriarch, instead of spawning more often).
 * Eagleland Osmosis: Inverted. Suburbia, the only official map confirmed to be outside of the UK (It's in an American neighborhood), has British license plates on some cars and some other out-of-place stuff. This is due to reusing assets from other maps which, as mentioned, take place within the UK.
 * Emergency Weapon: Besides your starting nine-millimeter, you also always have your knife. Its effectiveness is limited, but the "alt-fire" heavy blow can behead weaker enemies in a single stroke and in the hands of a Berserker, it can be dangerous.
 * Enemy Chatter: Every enemy has a voice. Not always a clear one, but every enemy says something.
 * The Engineer:
 * The Support Specialist perk has elements of this, making you much more effective with the welding tool. (Though you also get bonuses to Shotgun use.)
 * In the background, DLC character Aldridge worked on the assembly lines at Horzine. He was paid triple the normal wage for someone of his status and didn't ask questions about the weird goings on - until a Specimen broke open the door to his office. At that point, as it says in his bio, "lunchtime was over."
 * Evil Laugh: "Hahahaha, FEAR ME!"
 * Exactly What It Says on the Tin: Suicidal mode. See also Harder Than Hard.
 * Excuse Plot: So there's a scientist who's mad with grief over the death of his son, and he's been hired to create an army of supersoldiers, but his project gets shut down, so he experiments on himself, and... ah, the hell with it. Guns good. Monsters bad. Apply the one to the other. Get money. Buy better guns. Kill the boss. Repeat from step one.
 * Expendable Clone: The original purpose of the experiments was to create an army of disposable clone soldiers.
 * Expy: The Bloat is pretty much the Bloated Butcher from Blood with a dash of exploding on death a la Left 4 Dead's Boomer.
 * Flawed Prototype: All the specimens are failed attempts at creating supersoldiers.
 * Football Hooligans: Chopper Harris, a soccer enthusiast with a long police record of beatdowns taken and given. As far as he's concerned, the mutant apocalypse is just business as usual - only now he gets to use guns.
 * Fragile Speedster: The Crawler and Stalker are both fairly fast, but both have almost no health.
 * The Berserker perk has shades of this. Though he actually takes less damage than others, he also needs that to survive in melee combat. And he's faster than other perks.
 * Freak-Out: Mike Noble had one at a rave party after the specimens munched his girlfriend. He grabbed himself a katana and went to town.
 * Freudian Excuse: The only things Dr. Clamely cared about were work, and family. And then his son was shot through the head in a robbery... thus beginning his interest in "neurological redundancy".
 * Friendly Fireproof:
 * Friendly fire is off by default. It can be turned on, however, and your weapons are just as dangerous to teammates as to specimens.
 * Specimens can kill each other however. There is an achievement to get the Bloat to do this. The Fleshpound can too, as it charges through its own in an attempt to kill its target.
 * Like Team Fortress 2, even without friendly fire players can easily kill themselves with explosives. To a lesser degree, fire-based weapons also hurt the user if used carelessly. Naturally, perks based around these weapon types take less damage from them, but a demolitions expert can still easily blow himself up by accident.
 * Full-Frontal Assault: Except for the Stalker, Scrake and Patriarch, the specimens are all bare-ass naked, though with no visible genitalia. A close look at some of the models shows that the dangly bits were apparently surgically removed.
 * When going through the game files and code, it comes to light that the Stalker was supposed to be naked. Something involving Executive Meddling forced them to wear black lingerie.
 * Game Mod:
 * Started out as one. Then the guys who did Red Orchestra: Ostfront 41-45 (itself a Game Mod at first) were impressed and offered to make it a real game.
 * Later got one of its own, Defense Alliance 2.
 * Genre Savvy:
 * Upon Crawlers appearing, characters will sometimes say "Oh great, creepy crawlies. I guess they hop, too".
 * When the Sirens begin to appear, characters may say something to the effect of "Crap she's ugly. For god sakes, don't let her scream."
 * The trader frequently advises players to get close to her next location near the end of the wave, which is a smart thing to do if you want enough time to consider what to buy. Or, in some cases, get any time to shop at all.
 * Give Me a Sword: Don't have the dosh for a bigger gun? Ask your friend for the cash - or just ask them for the gun! Can be done literally by dropping a katana or claymore and letting another player pick it up.
 * Guns Akimbo: You can buy two 9mms, Handcannons or .44 Magnums, but it makes it harder to aim since when trying to look down your iron sights, you have to eyeball where the center of the screen is instead of just lining up the sights.
 * Hand Cannon: The Handcannon.
 * Half-Human Hybrid: Masterson is this. Thankfully, he's still willing to shoot zombies in the face. This also goes for DLC character Security Officer Thorne, who is visibly mutated unlike Masterson. Apparently he underwent modification for the pay bonus. He seems to want to take a bite out of Dr. Glover.
 * Harder Than Hard: In the first Christmas update, a difficulty above Suicidal was added, Hell on Earth.
 * Healing Shiv: The MP7 and MP5 are borderline examples. They are otherwise regular guns whose Secondary Fire mode launches a healing dart. Unlike the bullets, the darts are not Hit Scan and therefore it can be difficult to hit your teammates, especially when they're strafing and jumping around avoiding the Specimens.
 * Heroic Sociopath: Several characters seem to be this, according to their bios. Joining their number is Kerry Fitzpatrick, an escaped psych-ward prisoner who put the hurt on the specimens after they put the hurt on his guards. He's probably stretching the "heroic" part.
 * Hoist by His Own Petard: The Demolitions perk grants resistance to explosives in general, meaning that a high-level, armored Demolitions man can survive a near-miss from a Patriarch rocket. However, when that same rocket sympathetically detonates all the pipebombs the Demolitions expert has carefully laid out to kill the Patriarch... not so much.
 * Same thing may happen when the Patriarch rushes into the minefield and the Demolition expert is standing too close still.
 * Similiarly, the Patriarch can hurt himself when trying to blow open a welded door with his rockets.
 * Hold the Line: A common plan in most levels since the Welder allows you to funnel zombies or hold them up by making doors impassable barricades that must be smashed down.
 * Holiday Mode: The Christmas event made all specimens Christmas-themed, such as Gorefasts made of gingerbread and exclaiming "Cholesterol doesn't kill people, I do!" There's also the appearance of three Santas - one playable, one replacing the Bloat, and the other replacing the Patriarch. However, the former appears to be a rather shoddy Mall Santa, the second seem to be clones of the real deal, and the later is a Killer Robot. All the above return for Twisted Christmas 2, which also features a new map, Ice Cave.
 * Hollywood Silencer: Averted. The Firebug's MAC-10 has an attached suppressor, but its actual firing sound is rather distinct. When it was first added, it sounded like the AK47.
 * Hostile Show Takeover: GLaDOS got in contact with Horzine, it seems, providing some cloning vats for the Specimens. Then she decided to test them.
 * Implacable Man:
 * The Fleshpound will not change targets unless it loses sight of whoever it was focused on. It will continue to chase and/or horribly mutilate its target through bullets, fire, chainsaws, rockets... and anyone unfortunate enough to be in its way, including other specimens.
 * Note that none of the specimens will actually run away, but most will actively change target or respond to damage.
 * On lower difficulties, a fully-leveled Medic or Berserker player counts as well.
 * Implausible Fencing Powers: At higher levels, the Berserker perk allows you to extend ZED-time through kills.
 * Incredibly Lame Pun: A few of the achievements come to mind...
 * Random AXE of Kindness. Kill 15 enemies with the Fire Axe in a single wave.
 * The L.A.W. That Broke The Camel's Back. Deliver the Killing Blow to the Patriarch with a L.A.W. Rocket.
 * Quite a few of the Circus Patriarch's lines, too. "Ladies and gentlemen, we hope you enjoyed the show as much as we did! You might say... it was to die for." "It's time to knock 'em dead!" "Enough clowning around!"
 * The Circus Husk's lines are full of bad puns. "Fire is the hottest new item of the season." "Please remember that there is to be no smoking while the show is in progress."
 * Some of the Circus Scrake's lines, too. "What manner of monkey business is this?"
 * "This shit is bananas!"
 * Infernal Retaliation: Most of the stronger specimens have a lot more health than the Firebug's weapons of choice can chew through, requiring considerable time and ammo to put even one Scrake or Fleshpound down. And in the Scrake's it'll be more likely to trip his charge threshold long before he burns to death. The newer fireball weapon can charge up a more potent blast, but without a low difficulty and a high perk level, a single fully-changed shot still won't be enough to put down Scrakes or Fleshpounds.
 * Instant Win Condition: When the Patriarch dies, all other Zeds immediately stop moving and attacking.
 * Interface Screw: Crawlers will blur and darken your vision if they hit you, Stalkers will paint your display blood red, Bloats will stick a gooey substance all over your screen, and Siren screams essentially give you heavy myopia while they last. Even getting bitten by a Clot disturbs your sight more than you might expect.
 * Intrepid Merchant: DLC character and Action Survivor Mr. Foster is apparently this, in a similar vein to the Trader herself. He also sung at "London's premiere karaoke bar" on the side. He was writing an autobiography and laments the deaths of England's publishers, as doubtless the chapter he is writing about his fight against the Specimens would probably have been a good read.
 * Invisible Wall: Often to keep you out of Specimen spawn points, but most of the official maps don't have too many.
 * Jack of All Stats: The Commando has elements of this. He reloads any gun faster, can see enemy health and cloaked stalkers, and can chain ZED Time extensions. He uses the general-purpose assault rifles and tears though the swarming smaller Specimens. He lacks heavy punch though, and is less effective then The Berserker, Demolitions or Support at taking out heavy zeds.
 * The Support Specialist also count in a sense, as he can carry more equipment than most, including extra grenades. However, his versatility depends on his gear, whereas the Commando has all his perks already available with the default pistol.
 * Katanas Are Just Better:
 * Fast and lethal, though not quite having the bite of the chainsaw.
 * Mike Noble has a preference for these, according to his bio.
 * Kill It with Fire: The Firebug perk's job.
 * Knife Nut: The Berserker can chew apart early wave enemies with nothing but the weapon he spawned with, and get away with it.
 * Leeroy Jenkins:
 * Doing this is a good way to get killed. Unless you're a Berserker, in which case it's the whole point.
 * In his bio, Trooper Clive Jenkins is this.
 * Lightning Bruiser:
 * There's the enraged Fleshpounds of course, and Scrakes with low health tend to charge the player at high speed and chainsaw them to bits.
 * Then there's the Patriarch, who gains an enormous boost in movement speed upon turning invisible and frequently uses this to charge towards players who can't see him and strike them with an outrageously powerful melee attack that kills unarmored players instantly on higher difficulties. The Patriarch actually teleports when invisible, proven by him bypassing welded doors entirely.
 * Recent patches have turned every single Gorefast into one of these - despite their low health (relative to that of the others listed here), they can easily outrun the player and no longer have to stop moving to swing their arm blade. Multiple times.
 * To a lesser extent, the Berserker is second-fastest class in the game, enjoys a nice damage resistance, and deals out heavy damage with melee weapons. Also, an adventurous high-level medic is even faster, and with armor and the right hardware can dish out heavy damage.
 * Luck-Based Mission: A few of the Twisted Christmas achievements rely entirely on how generous the AI feels rather than any skill on the player's side. For example, one requires the player to kill three Bloats with a bullpup in one wave. With anything less than a full server, the game will barely spawn three Bloats per match if anyone tries to go for it.
 * Commando perk progression depends on Stalker kills with assault rifles, which pretty much only Commandos ever use. A lot of them actually. The amount of stalkers spawned per game varies wildly. Even if a lot spawn, its almost certain another class will kill them before you do. Although commandos at least get to spot them more easily, but that won't help much when the Stalkers come among a crowd of other specimen everyone is firing at. They are pretty frail, too.
 * Mad Doctor: The Patriarch. According to the MODDB entry, he became obsessed with his work.
 * The Summer Sideshow event mentions that Kevin Clamely had an equally-insane great grandpa named Errol Clamely, and that either him or young Kevin were responsible for the Zed freakshow.
 * Made of Iron: Most of the bigger, badder specimens can take stupidly large amounts of punishment, but the Siren in particular is odd - while she can't take as much as Scrakes or Fleshpounds, one would think an anorexic-looking crazed girl in a straitjacket would have less health.
 * Made of Explodium: The Bloat usually explodes when killed. Many parallels are drawn to the Boomer.
 * Although he's more like the Spitter, using acid rather than an otherwise harmless liquid that attracts more enemies.
 * Made of Plasticine:
 * Clots, Crawlers and Stalkers have little to no health, and most specimens lose limbs very easily. Players also tend to take lots of damage, but you do have the ability to heal yourself and each other.
 * ZED time seems to make heads popping or limbs detaching more spectacular.
 * Make Me Wanna Shout: The Siren attacks via a horrid scream.
 * Meatgrinder Surgery: Implied. According to its bio, the Scrake was designed as a medic. So why is it carrying a chainsaw?
 * The Medic:
 * The Field Medic perk makes you this, of course.
 * Alfred Anderson is this in his bio, he was a paramedic at a London hospital.
 * Mighty Glacier: The Fleshpound is crazy strong and can take multiple rockets. He's also easy to run away from...until you piss him off. And running away is one of the ways to piss him off. And once he gets pissed off he becomes something else entirely.
 * Monster Clown: What the Bloat and Fleshpound were reskinned as for the Summer Sideshow event.
 * Never Split the Party: While not as bad as some other games, going off by yourself is a good way to get mobbed and therefore killed. In addition, it's extremely difficult to kill even a single Fleshpound or (after patches) Scrake without serious injury or death. It doesn't help that the toughness of the monsters/the strength of their attacks increases at a far faster rate than the raw strength of your party.
 * And you can't heal yourself very well. Not even as Field Medic.
 * Night of the Living Mooks: The entire game, pretty much. Although they're not technically undead.
 * No Fair Cheating: Perks are disabled and unable to be leveled up if a game has any mutator that only spawns low-level mooks enabled.
 * No Hero Discount: Logically, the Trader's life should depend on you killing the hordes of bloodthirsty specimens overrunning the area. Apparently that isn't quite enough to warrant a discount. Subverted in that you do get discounts for certain weapons depending on your chosen perk and its level.
 * Not Using the Z Word: They're "specimens." Justified in that they're military clones turned into brain-dead cannibals. Funny enough, the official nickname for the specimens is a Zed. Absolutely no one calls them that, in-game or out.
 * The player characters actually do refer to them as zombies on occasion. Granted, it's always to call them inferior zombies.
 * Offscreen Teleportation: The spawn points of Specimens is basically wherever a player isn't looking. Even directly around the corner behind you.
 * This poor guy had a Fleshpound spawn directly behind him.
 * Oh Crap:
 * Essentially the reaction whenever the Patriarch spawns in the opposite direction from where the players set up their wall of pipe bombs. Doubly so if he spawns in the middle of the group. It does happen sometimes.
 * There's a voice command specifically aimed at vocalizing this sort of reaction. "We're screwed! Leg it!"
 * "One in the pipe!"
 * One Bullet Clips: Played straight, though the HUD only shows the number of magazines you could fill with the number of bullets you have. This excludes the pump-action and double-barrel shotguns, the lever-action rifle, and the crossbow, which load one round at a time.
 * Oddly enough, you can't reload the double-barrel shotgun after firing only one barrel.
 * Our Zombies Are Different: Instead of the living dead, they're clones meant as military cannon fodder Gone Horribly Wrong.
 * Poison Is Corrosive: Bloat acid is marked as poisonous by the game tips. However if you're killed by being puked on, the death message reads: "X was corroded by Bloat acid".
 * Police Brutality: Constable Briar apparently has a history as a riot cop of "bludgeoning hippies" and "manhandling environmentalists." Such tendencies serve him well against the Specimens.
 * Powered Armor: Horzine Industries was apparently publicly developing a next-generation suit of combat armor simultaneously to the Specimens. Agent Wilkes, DLC character and British Overt Operative wears it, having secured it from their labs (though it offers no in-game benefit). According to his bio, Horzine "was great at multitasking." Security Officer Thorne also wears what looks to be the same armor minus the helmet and most of the arms.
 * Power Limiter: That...glowy thing...on the Flesh Pound's chest is constantly pumping it full of depressants, sedatives, tranquilizers and the like. However, if the apparatus senses from its vitals that the specimen is in danger (normally from itself and its own temper), it'll stop with the downers and start pumping it full of adrenaline and stimulants.
 * Pre-Mortem One-Liner:
 * "One in the pipe!"
 * "Wait right there, I'll make this quick!"
 * The Robot Santa version gets a few new such lines - "And not a creature was stirring, because they're all dead! Ahahaha- eh, ho ho ho ho ho!"
 * Real Is Brown: There are shades of brown basically everywhere in a map. Some custom maps made official through patches are more colorful, though.
 * Reality Ensues: All the specimens are recipients of an experimental process that enables them to survive absurd/fatal levels of nervous damage and keep on trucking, in addition to other unique survival mechanisms. Where this trope kicks in is when it turns out that for all the genius engineering, military hardware and bladed implements can still liberate them of their heads, and while they don't die from that, they still bleed to death within a few seconds.
 * Replacement Goldfish: Several million inhumanly tough deformed murderous goldfish.
 * Revolvers Are Just Better: Twisted Christmas 2 brings a .44 magnum revolver for the Sharpshooter. It can be dual-wielded, like the other pistols.
 * Reward From Nowhere: You earn dosh by killing zeds. Where it actually comes from is a secret to everybody.
 * All things considered, judging from how it jumps up if you survive the wave, it may be a credit the merchant is giving you. The actual thrown money is probably just a graphic representation of donating funds to friends.
 * Sexy Santa Dress: During the holiday event, the Stalker wears a very skimpy Santa Costume.
 * Short-Range Shotgun: Zig-zagged - the pump-action and combat shotguns are rather effective at longer ranges, but the AA12 and hunting shotgun are too inaccurate to use past close range.
 * Snake Oil Salesman: The Mechanical Man (Summer Sideshow version of the Husk) is a robotic version of this trope. His product is fire.
 * Sniper Pistol: The first shot is pinpoint accurate for most weapons, notably with the handguns (Even when dual wielding!).
 * Sole Survivor: Private Schnieder's squad was wiped out shortly after they were deployed. He had two options. Die alone, or shoot, stab and bludgeon his way to survival. Guess which one he picked.
 * So Long and Thanks For All the Gear: If a player leaves mid-game, all the money and weapons they had disappears with them. Nicer players tend to at least donate their best gun to a teammate before they leave, though.
 * Soundtrack Dissonance: The Christmas event map has you killing Zeds while the music from The Nutcracker plays in the background.
 * Steampunk: The prize for unlocking 10/13 Summer achievements is a steampunk Mr. Foster skin.
 * One of the prizes from the Steam Summer Sale (which can still be purchased otherwise) was the first Steampunk character pack, and as of Twisted Christmas 2 there is a second pack. Each of these new characters is identified by a particular class and even has the in-game class symbol on one arm.
 * Reggie: A brutal ex-cop with a custom-made suit of scrap metal armor.
 * Adam: The world's foremost Pyromaniac-for-hire, whose obsession saw him switch orphanages and later, prisons, alarmingly often.
 * Doctor Dave: A Back-Alley Doctor with a Nice Hat.
 * Peter: A career assassin, descended from a long line of such, and slightly concerned that the mutant masses may be too much for even him.
 * Quentin: Lifelong demolitions expert, former military man, accidentally blew up a superior officer's dog. He thinks he can make up for that by cleansing England of the Specimens.
 * Harold: Former relationship councilor. Now that all his customers are dead, he's tapped into his dark side in fighting the specimens, and he's kind of scared of it.
 * Phil: Former supermarket shelf stocker, but he tells people he's ex-special forces. But because of his excellent workout routine and the fact that he played a lot of FPSs and read a lot of gun magazines, he's actually pretty good at killing Specimens.
 * And special guest, Steampunk DJ Scully! He's still pissed about the Specimens ruining his first big DJ gig.
 * Stuff Blowing Up:
 * Leave this to the L.A.W. and the plentiful grenades.
 * The Demolitions Perk and its two dedicated grenade launchers, plus an underbarrel one on the new M4 Carbine.
 * Survival Horror: The game bills itself as "co-op survival horror" and the monsters are scary enough, but the plentiful ammo, health, and levity keeps the proceedings from getting too frightening.
 * Take That: One of the Taunt Button insults is "you're pathetic... like a bunch of bloody Millwall fans!"
 * Twisted Christmas 2 adds, along with two versions of the American M4A1 carbine, an achievement titled "Bloody Yanks" for expending an entire magazine but only killing a single specimen with it.
 * Taking You with Me: See Desperation Attack.
 * Taunt Button: With just a few short keypresses, you can insult your opposition ("You couldn't scare my mum!")... or your allies. ("I've met smarter donkeys than you lot!")
 * Title Drop: Descriptions for community-made maps tend to shoehorn these in, regardless of whether the resulting phrase makes any sense with context or not.
 * Turns Red: The Flesh Pound literally turns red when he enters attack mode.
 * Up to Eleven: The Fleshpound's aggression levels can apparently go this high, according to it.
 * Unbreakable Weapons
 * Unusable Enemy Equipment: Understandable, given that the few specimens who have weapons have them grafted on. This did not stop the Husk's Fireball gun from becoming a usable weapon, as of Twisted Christmas 2.
 * You still can't take it from a dead Husk, but have to buy it.
 * Violation of Common Sense: Confronted by a giant cannibalistic super soldier with a chainsaw for a hand? The best course of action is to engage it in hand-to-hand combat.
 * Strapping several proximity bombs to your face is... surprisingly effective.
 * Visible Invisibility: Stalkers have a shadow, even when they're cloaked. Alternatively, if you're a Commando, they appear as a bright red form when they get within a certain distance.
 * "Wake-Up Call" Boss: Most new players underestimate the Fleshpound.
 * What Do You Mean It's Not Awesome?: This tends to happen a lot when some other player activates ZED time. The slowdown doesn't make reloading, walking, or welding a door any more impressive. It still gives the sort of accuracy bonus you'd expect from bullet time, though.
 * White Gang-Bangers: Kevo the Chav, a slacker who spent most of his time drinking cheap lager and trying to work up the stones to shoplift. He was as surprised as anyone else when he found himself fighting a tide of angry mutants - and surviving.
 * X Meets Y: Left 4 Dead meets 28 Days Later (according to IGN).
 * It's more like Left 4 Dead meets Team Fortress 2 meets Fallout 3.
 * Actually, it's more like Left 4 Dead meets Counter-Strike in Britain.
 * You All Look Familiar: The specimens. Handwaved with cloning.
 * Your Head Asplode: What happens if a Siren kills a player with her scream.
 * Zombie Apocalypse: More or less.
 * Zombie Gait: How Clots and Bloats move around. Gorefasts too, until they get close.

"I'm cutting this one open, lads!"