Script Breaking

""You used your escapipe! Normally a smart move, but now I'm afraid the game can't be continued. Please press the Reset Button and try again.""

- The King, Phantasy Star 3, after you escape from prison the unauthorized way.

Most kinds of games rely on a certain set of triggers and rules to regulate the progress of the scenario and check whether certain conditions are met. In addition to triggers and rules, there are also implicit assumptions about the state of the world. That certain entities are still alive. That the player cannot reach spot X without having done task Y. These are usually collectively known as the game's "script".

Often, particularly in games that allow a significant amount of free-roaming, if one attempts to do something that would make sense in the real world and/or within the game world, and that is technically allowed by the rules of the game, one will find that the game is not robust enough to cope and one will get stuck, be forced to go back or find that events play out in an illogical fashion. This typically happens by violating one of the assumptions about the state of the world. Killing an entity that the game needs later, using Sequence Breaking to reach location X without having accomplished task Y. And so forth.

It is also common to experience this if one cheats, particularly by trying to create a specific condition without the proper prerequisites having been met.

These situations often occur when the player tries to do things the scenario suggests is possible and even reasonable, but which the game rules cannot account for.

See also But Thou Must!. For the idea of "breaking" a script in the writing process, see: Script Life Cycle. The polar opposite of this trope is The Dev Team Thinks of Everything. Often coincides with Sequence Breaking, which deals with the intended sequence of gameplay elements rather than the logical cohesion of the narrative, since breaking one of these tends to break the other as well.


 * The Operation Flashpoint single-player campaign features at least two instances of this:
 * In one mission, the player character is captured as soon as he reaches a particular area. It is possible to kill the enemies that do the capturing if one throws grenades into the area where they stand, in which case the cutscene will still play out, but the captors will be corpses lying still on the ground.
 * In another mission, the player must attempt to slip a lorry full of partisans through an enemy control post. If one goes along with this, there is a scripted confrontation and one is forced to escape on foot while being pursued by enemies. Yet if one takes the lorry off-road before the control post, one can drive through the forest and reach the final destination without incident. At that point, the game's script forces the passengers to get out and head back to the control post on foot, to fight a skirmish that was supposedly undesirable.
 * In the second-gen Pokémon games, using a "Walk Through Walls" Game Shark code and walking up to sprites you are not supposed to touch will either make the sprites say "object event" or crash the game.
 * The same thing happens in the first gen games too, and you can encounter some pretty bizarre glitch trainer battles with it. You can also break sequence in both Game Boy titles and get into pokemon battles without actually having any pokemon in your party, which also results in funky (and game-breaking) glitches.
 * In the N64 game Golden Eye 1997, the player can have much fun by exploiting the cutscenes with a cheat code that gives Bond an unlimited supply of every weapon in the game. The player can stop just short of the area where a cutscene will activate, load the area with explosives, such as proximity mines, and then step into said area, resulting in a cutscene where Bond will walk unscathed through an environment erupting in fireballs and sending any NPCs flying. Fortunately, this does not result in a mission failure if one of the NPCs killed was supposed to stay alive.
 * Also, fiddling with the second player controller, with the addition of luck, one can simply shoot down many of the cutscene characters. Causing, in one instance, the memorable scene of Bond in his Victory Pose with his Bond Girl Natalya dead at his feet.
 * It's also possible to kill every named baddy in Golden Eye 1997, whether or not they are supposed to die at that point. Generally, though, you can only get away with killing Ourumov without failing your mission. Unfortunately, the storyline never changes.
 * Baron Samedi, in particular, can be killed in the ending cutscene of his level. During his maniacal laughter.
 * In Soldier of Fortune, there are numerous instances where an enemy scripted to fall from a perch in a sniper's nest when shot can be shot by the player before he's in position, resulting in the enemy character displaying the "falling" animation anyway, even if he's already on solid ground. Some enemies can likewise be shot by alert players before the game intended, after which they calmly proceed to their next scripted checkpoint missing arms, legs, or even heads. Only upon reaching said checkpoint do they apparently realize their wounds and expire. It is also possible for a sufficiently skilled or determined player to snipe the pilot of a helicopter carrying a pallet of crates meant to take off and leave immediately after coming into view. If the pilot is shot in this very narrow window of opportunity, the helicopter crashes while the crates continue up and away.
 * In Deus Ex, the player, attempting to escape New York by catching a helicopter in Battery Park, is met on his way out of the subway by an overwhelmingly large enemy force led by a character flagged as invincible. There are several ways to sneak around the group without being caught, but even if you get to the helicopter, you can't take off -- the game requires that you be captured. Earlier in the game, it is possible to go from a bar in which the pilot of the helicopter that transports the player is drinking to another area, complete the mission there, have him arrive in the helicopter for pickup, and through creative use of crates jump back over a fence and make it back to the bar, where the pilot can still be found. There's also various Boss Battles that can be completely skipped if the player manages to kill his enemy before triggering the cutscene (usually by approaching said enemy) that initiates the battle.
 * DX has been hilariously, systematically broken by some of its more "devoted" fans.
 * Subverted with Anna Navarre. The smartass player wanting to break the script by killing her before she starts her dialogue (by placing a mine on the entryway) will cause the game to proceed exactly as you'd expect in the event of Navarre's murder.
 * Killing such people as Joe Greene and the caretaker before you're asked to results in JC Denton telling them he offed them already - Dowd and Philbin will remark that you're Properly Paranoid.
 * In Hitman 2: Silent Assassin, it is possible to kill the final boss by strangling him with a garotte through a wall. If you do this, then the cutscene before the boss fight will show a shotgun floating in mid-air, and during the battle you'll fight the boss' flying corpse.
 * And if you strangle him after the boss battle start, he will be on the ground in a HUUUUUGE puddle of blood. The Dev team assume you would shoot him with the M60 or another really heavy gun.
 * In Baldurs Gate a character called Biff the Understudy will appear to deliver the lines of characters that have been killed prematurely.
 * In Half Life, near the beginning of the game, the player climbs a ladder to see two zombies fighting a security guard. The guard talks to the player upon seeing him. A particularly lucky and/or skilled player can shoot the guard to kill him as soon as he begins delivering his line, therefore causing the guard's corpse to speak.
 * A more serious one occurs when Freeman gets captured. In older versions of the game, you may break the script if you try moving around during the cutscene, leaving you in a dark "script-holding" room which you can't escape from.
 * Sequence breaking is possible in certain Castlevania games. A glitch in the recent Castlevania Portrait of Ruin makes it possible to enter a cutscene room from the wrong side -- in which case the scene still happens, but with you standing behind the bad guys, who don't turn around. The fact that there are gestures in this scene makes it even more surreal.
 * In Zork III, grues prevent you from going into dark places; this normally justifies the need for a lamp, but one place was blocked by a lake that extinguishes your lamp, requiring you to find Grue Repellent. However, in early versions of the game you could put the lamp inside a chest and take it to the area without being extinguished. Strange because the unintended, script-breaking activity also happened to be perfectly logical--of course putting the lamp inside something keeps it from getting wet.
 * Somewhat famously, in The Legend of Zelda: Ocarina of Time, the game only checks for completion of two of the five "adult" temples. By abusing certain bugs, the savvy gamer can complete the Shadow and Spirit temples without completing the Forest, Fire or (frustratingly obnoxious) Water temples and then gain access to the final temple. The game assumes that you have completed the other three.
 * Temples are for sissies. It's possible to beat the game while skipping all 5 by glitching items into your main hand and capturing stuff in bottles to overwrite the quest flags.
 * In Chapter 2 of The Magic of Scheherazade for the NES, you're supposed to fight through the Chapter, bouncing back and forth between the present and the past, going through caves with invisible pits, with the goal being to ultimately acquire a character who can guide you through the Maze Desert, a Lost Woods sort of area, to the Palace of the boss of the Chapter. Problem: The sequence through the Maze Desert is always the same, and the game doesn't bother to check to make sure you actually acquired said guide character, making it possible to skip most of the Chapter and go directly through the Maze Desert to the Palace. It's clear Culture brain never bothered testing this scenario, as the characters you skip by doing this show up in any post-Chapter cutscenes (But, oddly enough, not in the RPG battle sequences. In fact, you can't even select individual characters you acquire later in those sequences--you have to select their Formations; the game won't scroll past the "holes" created by the missing characters). Given the game is pretty good about checking for other breaks (The funniest "You can't do that!" message is probably "You don't have enough friends to defeat Troll"), this specific one is rather surprising.
 * In Star Wars: Jedi Knight II if you kill Tavion not the usual way, by accumulating damage, but by tossing her off a cliff (ridiculously hard to do, because they were almost always immune to Force Push) the cutscene that plays afterwards, where Kyle is supposed to threaten Tavion, plays out as normal... except without Tavion. At one point, Kyle is suspending Tavion in mid-air with the Force Choke ability, thinks better of it, and drops her. At which point Tavion fell out of midair, back into the scene.
 * This is even harder to do than one would initially think. To prevent premature ending of the battle by dropping Tavion off the cliff, there are walls at the edge that only work for NPC's unless said NPC's are dead. So, to actually push her off the cliff, one must kill her from damage and then get in a force push as the cutscene starts.
 * There is actually a much simpler, if idiotic, way to pull this off, and the best part is that it's entirely Tavion's fault. One simply has to get onto the highest point in the stage, which is, if I remember correctly, a container stacked on top of another container, and crouch. Tavion will jump up to get to you. Getting under her at the correct angle will result in you getting goomba-stomped... and Tavion sailing off the edge, where you can get in that last force push as she dies from the falling insta-kill.
 * In the Free Space series of space sims, events are usually triggered by the presence or the absence of a certain ship. To prevent Script Breaking, mission designers often make script-important ships invulnerable, or cause them to self-destruct if the mission doesn't go out as planned. The "fix" itself causes certain problems, for example, a player manages to immediately disarm an enemy capital ship that was supposed to destroy a friendly target, the friendly ship will still give out a mayday call and blow up anyway. Other times, during an attack that's "impossible to repel", the invulnerable or self-destruct events are not included because the mission designer is confident that the script will go out as planned anyway. When the "impossible" event happens, and the player managed to fend off the three dozen Goddamned Bats and successfully defended the disabled friendly cruiser (that was destined to blow up), the mission just freezes. Or maybe the rebel cruisers that are "no match" for the gigantic GTVA Colossus get in its blind spot and slowly chip away at it until it blows up. Script Breaking in Free Space will have ship commanders talking from the dead, or from subspace, or the action just stopping and never getting the "Return to Base" order.
 * In Freespace 2, there's a mission where you're supposed to destroy some of the Sathanas' main guns to give the Colossus a fighting chance. It's possible to destroy all guns, which makes the next mission hilarious: The Colossus sticks to it's script and delivers paniced damage reports even if it's receiving no damage.
 * Actually not true in that case, the damage reports are because the ship was over loading its beams to the point of melting themselves so it makes sense that the crew is panicking over their melting ship.
 * There is also a slight subversion in Freespace 1 in the first mission where you encounter the Shivans. If you manage to destroy the Shivan ship that's supposedly out of your league, you'll get a medal and a special mention in the debriefing.
 * Space sims in general have notoriously bug-prone objective systems, usually don't allow in-mission saves, and often change objectives in mid-mission or vaguely state mission objectives to begin with. This can lead to a lot of Guide Dang It moments where the player isn't sure if they're failed, succeeded, or if the game has bugged out on them.
 * With the use of a cheat code in Grand Theft Auto 3, a player can use cars as flying vehicles. If the player manages to master the controls of the vehicle, they can fly over the broken bridge that they start at in the beginning of the game, causing the script to completely skip the first third of the game.
 * It's possible to skip the second island as well, with some creative use of boats (you can't get a boat over the pipes in the sea, but you can beach it and push it around on land... and back into the sea again).
 * It's possible to cross the broken bridge immediately with some creative jumping (at least on the PC version), and if you ram a car into a moving subway train in the right part of the second island you can pop back up on the third island.
 * This was averted in San Andreas; there are several ways to get to the blocked areas, but since you can't buy any property or enter any shops, all you'll be doing is running from the cops.
 * This happens in Phantasy Star 2 if you kill the security bots coming to arrest you by cheating, after which you can no longer progress through the plot.
 * This becomes far worse if you get afflicted with a glitch in which you get into a random encounter at the same time those things should attack you (win and you're stuck). Beyond frustrating if this occurs on a first playthrough.
 * The infamous "Red Key Card bug" from Little Big Adventure / Relentless is caused by Script Breaking. Normally, in order to break into the museum, you need to get said key card from a character and use it on the back door of the museum to get in and do some stuff here (including stealing several items). However, it is perfectly possible to steal these items by just fighting your way in from the front door, and if you do this, the game will assume you already have the key card, so you can no longer get it. The nasty part is that you'll need the card later on and won't be able to complete the game without it.
 * In the final mission of the single player campaign in Age of Mythology, you are supposed to get Arkantos turned into a demi-god and have him kill a statue of Poseidon. By using cheat codes, you can just cast tornado repeatedly on the statue until it dies, at which point, sure enough, there's a cutscene of demi-god Arkantos fighting and finishing off the statue.
 * If you're good, you can also get it by just building a very large, very good army.
 * Siege units in particular work well. It is a statue and therefore very similar to a building in terms of damage resistance.
 * The first-person-shooter Red Faction had rebel miners that were scripted to be killed by certain guards, either through grappling or general combat. Killing said guards before they could kill the miners (or were in the process of), would often cause the miners to grapple with 'invisible' enemies while the guards' corpse lay at his feet, or merely fall down dead when reaching the end of their script.
 * Several first-person-shooters (including Red Faction and Command & Conquer: Renegade) have dying allies who are scripted to deliver a message and then expire. Since these scripts are uninterruptable, the player character can freely wail on the dying soldier/medic/civilian/scientist with any weapons he has available, while the poor schmuck continues delivering his important dialogue. Half-Life features a similar situation, with scientists and guards who are supposed to remain in sitting, lying, crouched (or otherwise immobile) positions (and usually deliver a Message Of Importance). When given a whack with the crowbar, they will ignore their previous script, stand up, and perform as any other instance would.
 * In the Elder Scrolls series, the third game, Morrowind, is (in)famous for its many bugs. Being a sandbox game, the player can kill pretty much everyone. Inevitably, a main quest-critical NPC could be inadvertently killed by the player. Usually, killing an important NPC will display a small message indicating that the main quest is now unbeatable. However, many lesser NPCs do not display that message when eliminated (try killing members of the three houses, such as Dren).
 * Averted in the sequel, Oblivion. Important NPCs cannot be killed, only temporarily knocked unconscious. While the game cannot be rendered unwinnable, it also lost much in immersion.
 * Bethesda made the main quest script more flexible, so that it can have multiple entry points. This allows experienced players to skip ahead of the hoop-jumping-intermediary-fetch-quests, or psychotic players to shoot 'em all as they go, but has surprised exploring first timers who weren't expecting to stumble back into the plot.
 * User-created mods are sometimes plagued with "talk triggers" not activating. When the player is meant to be able to advance conversation with an NPC, they are given a "talk trigger" to ask something new. These can break -- by no fault of the player -- rendering the quest impossible to continue.
 * In the fifth game of the series, Skyrim, it's possible for this trope to occur when first entering Solitude.
 * At one point in the FPS Shogo Mobile Armor Division, the player finds himself in an underground tunnel, where proceeding forwards will trigger a cutscene where an enemy appears, runs off, and causes the tunnel to cave in by exploding it. However, careful examination of said tunnel reveals a logo of Monolith (the game's creators), which when shot causes the same explosion, making the cutscene look totally wrong as a result.
 * In Half-Life 2, at one point the player runs across a courtyard dodging fire from a huge disintegrator ray. When the player rushes into one of the buildings, they'll see a man behind prison bars get shot to death by some Combine. If the player is lucky/skilled enough and fast enough, they can kill the guards before they can kill the person behind bars. However, the NPC will crumple up and die anyway.
 * If you do manage to kill the Combine in time, the man doesn't die right away. Looking through the door at the correct angle will reveal that he is still very much alive - until you walk through the door and trigger his scripted death. Instant ragdoll.
 * Similarly in Half-Life 2, at one point the player will come across two men, on a rock, one injured. A small little scene will take place and summon three Antlions at once. If the player is extremely lucky and skilled, they can kill the antlions when they pop up before they are able to do anything, but the injured man will die regardless. I guess one of "the greatest minds of our generation" can not be saved.
 * By using a collision detection error, it is possible to get a few Pearls earlier than you're supposed to in Beyond Good and Evil. This isn't script-breaking in and of itself... But if you hunt for all the Pearls possible at that point in the game, it ends up giving you just enough Pearls to purchase the next hovercraft upgrade, the Jump Booster, which you aren't supposed to be able to do until after you've been to the Factory area. If you attempt to go to the next area, the Slaughterhouse, without visiting the Factory, the game gets rather confused--dialogue for Double H appears, even though he's technically still trapped in the Factory, referencing events in cutscenes you haven't seen, and Pey'j mysteriously vanishes. If you make it through Slaughterhouse Road and attempt to dock at the other side, the game freezes up--presumably because it has no idea just who the heck is your partner anymore. A video demonstration.
 * In Maelstrom, a rather poor and buggy sci-fi RTS, about the only interesting feature was terraforming : raising or lowering terrain. There were at least 2 moments were this could be used to screw with the game. In one mission the player had to move a group of units through a half flooded ruined city. The usual way was to use terraforming to create bridges between the small island in this area to go around and end up on top of a small cliff. Or, since the player had lots of energy resource, you could just raise a gigantic ramp to the top of the cliff from one of the first islands, bypassing a few event triggers and confusing this missions objective system. In another mission the player had to destroy a few alien bases in a mountainous region. The map was divided by a few mountain ranges with several valleys in them for ground units. Since the aliens have no terraforming or flying transports, the player could just raise walls in the valleys to cut of his part of the map from alien ground units.
 * In Ecstatica II, you were supposed to open the doors to the main hall by striking them with the rod retrieved from the top of the prison tower. However, it was possible to jump from the terrace above onto one of the balconies of the main hall and get in that way. However, you weren't able to get the doors open from the inside, and there were no other exits.
 * It's possible to finish Ultima VII, getting the last two prisms with script breaking, leaving Alagner alive and skipping the Time Lord.
 * 1) Trying to reach the square prism without protection subjects you to damage that eventually exceeds your maximum hit points. The Forge of Virtue add-on increases your maximum hit points but the programmers forgot to increase the damage done when you go for the square prism. Result: it's now easy to get the prism without protection if you heal yourself.
 * 2) The path to the round prism doesn't kill you if you don't have the needed items. It just sends you back. It turns out that repeatedly trying will eventually get you there anyway. This may have been an interaction between a fast machine and a slowdown program.
 * An annoying one in FEAR, though it got patched. There is one laptop in the entire game that is plot relevant, the rest are there for listening pleasure. The thing is, once you download the data from the laptop, you can't download it again. You also get to see this laptop and use it before said plot relevance is made. So when your CO asks you to download the data from the laptop, which you might've done already, you can't download it and complete the objective. Spend all the time in the world running around the map, but you'll just have to restart from your last save.
 * In Champions of Norrath, after defeating the Spider Queen Shelox, the player is supposed to enter the tunnel Shelox emerged from in a cutscene before the fight. If, instead, the player uses a Gate Scroll to return to the town to sell the loot Shelox dropped and then use the Portal in town to return to the Portal outside the bosses chamber, the player becomes stuck. The door into the chamber is locked for the fight and was originally unlocked during a cutscene by an escort character. There is no mechanism for the player to unlock the door from the outside, and Portaling back to town and using a Gate Scroll (hoping to return to where the first Gate Scroll was used, in the chamber) teleports you to the last place you were teleported...which is the Portal outside the lair. Time to restart from the last save...
 * Crafty players can jump down very deep pits in Halo to sequence break. However, more than sequence break, the player skips all the event flags in the map as well; Master Chief can trot to victory! Neither friend nor foe will spawn in the entire map due to the linear nature of Halo's event tripping.
 * In Halo 3's The Covenant mission, landing the Hornet on the Citadel can prematurely trigger the next chapter, and when you reach the point where the Flood team up with you, the game freezes.
 * Strife, the Doom engine RPG, is painfully easy to break. From minor and recoverable things like going back to break the illicit power tap (and failing a mission you've already completed) to major things like killing the Sigil piece holders in the wrong order, which makes the game Unwinnable. There's only two 'official' sequences, one for the happy ending and one for the Downer Ending, but you have access to two of the last four for the entire second half of the game and can theoretically kill them at any time. The game plays fine as long as you obey everyone's orders, but don't ever think for yourself.
 * Stranglehold checks to see if you've beaten a section by crossing a trigger. However, it checks for any trigger. One those rare occasions where you can go backwards through the level, it is possible to advance by retreating.
 * Kya Dark Lineage is susceptible to this, at least if you're able to engage in any Sequence Breaking at all. For instance, in the final area (the Wolfen Lair), you're supposed to progress through the level and get captured by the Wolfen, who will take away your weapon. This may not seem like much, but it's actually damned important. It is possible to get through the blocked door, over the top, and sneak in the back way. Clever, right? Wrong. The game was not at all prepared for this, and will still trigger the cutscene wherein Kya is caged up and unarmed- at least in theory. In practice, retaining your weapon through this sequence break makes the game Unwinnable, as you then have no way of accessing the command you need to get out of the cage once the cutscene is done. Admittedly, Sequence Breaking is made far, far more difficult (supposed to be impossible, of course!) than in games that reward it, but to not anticipate at all that some player would try it is just silly.
 * In the Starcraft mission "Agent of the Swarm" (the Zerg mission where you have to defend the Chrysalis until it hatches), normally you're supposed to wait until it hatches then infest a Terran Command Center, but there's nothing stopping you from just waltzing into the base and taking the command center as soon as the mission begins (although, through legit means it'll probably hatch before you get near the command center). This makes the conversation at the end of the mission weird since  hasn't hatched yet but they're talking to Reynor as if they already hatched.
 * In an early Terran mission, Raynor tries to stall a Zerg invasion until evacuation transports can arrive. Even if all the Zerg on the map are destroyed, the Terrans still leave at the end of the mission.
 * A justification is given beforehand, but still feels odd that nothing happens when you destroy the attackers and settle in to wait for the timer to run down with the threat of immediate attack averted.
 * They have to wait for evac to get there. Can't get off-planet without the proper vehicles.
 * Chrono Trigger encourages Script Breaking in the New Game+ to access many of the game's multiple endings, and can, in fact, legitimately allow the player to kill the final boss about 20 minutes after the introductory cutscenes. However, this does result in some bizarre dialogue before the fight, given that the party.
 * Tool-assisted run of the whole game from the beginning show how the storyline can be messed up to the point of the plotline being a complete mess.
 * In Fallout 3, if the player picks Mr. Burke's pocket before telling on him, he will repeatedly try and pull his gun of Lucas Simms, and if the player follows Lucas out of the bar, he falls over dead anyway. Lucas can be saved via other means though (Such as taking the hits for him and taking out Burke).
 * While perhaps not -script- breaking, it is possible to simply go to your dad's last location and do the final missions first. While this is a nice shortcut for veterans, a new player doing a certain side-quest will almost certainly trigger an event flag at around the half-way mark of the main quest, thereby accidentally side-stepping a huge chunk of the main campaign. It's somewhat immersion-breaking, at the very least. It's also awkward if you want to get all the achievements.
 * It's also pretty easy for a new player exploring the Wasteland (rather than following the main quest) to stumble upon his location, which doesn't even have a locked door to keep you out of it.


 * In The Legend of Zelda Majoras Mask, you can do this after you defeat a dungeon boss. You reset time back to the first day and warp straight to the dungeon and then the boss, after which characters who shouldn't remember who you are will act as though they've always known you. (However, this Groundhog Day Loop is a major feature of the game; once you solve certain quests and attain certain rewards, they stay solved and you keep the Plot Coupon even if you reset the clock again.)
 * In the original Paper Mario, using a hack to defeat Bowser during the unwinnable boss battle at the beginning will not only be script breaking but will break the rest of the game.
 * Players using the Mission Architect system in City of Heroes can learn first-hand what the developers have to go through to make sure that missions work properly, especially when trying to get fancy with chained objectives. If the script is not planned out well and tested it could end up making a mission near, if not actually, impossible to complete. The author needs to learn to think of everything that their players might do.
 * In Cave Story, you can actually get past Chaco's house in Grasstown without getting the Fireball by getting hit by a bat at a specific point in your jump, giving you recoil that is just enough to get on top of the house. However, doing so gets you stuck since not getting the Fireball makes it impossible to get the jellyfish dialogue from Chaco which makes it impossible to get Jellyfish Juice which makes it impossible to advance the plot.
 * In the free web game Realspace 2, there is an opening cutscene of the enemy ships attacking a smaller set of good ships and then they attack the planet the good ships protected. The trouble? Not all events were actually scripted. The game simply spawned the necessary number of ships and had their AI's battle. But once in a blue moon, the good guys overcome the odds, destroying every enemy. The game stops there, the rest of the events never happen. Luckily this was an intro that could be skipped so the game didn't break. Notable for not requiring the player to do anything for this to occur.
 * In Earthbound, it's possible to glitch through certain walls and walk directly to any location in the game. At some points, the game assumes certain characters are in your party whether you've met them or not (even if Ness is alone when he's captured in Threed, Paula appears when Jeff rescues him; Poo appears when Ness returns from Magicant). However, you can't simply walk through walls to the final boss; you have to use the Phase Distorter to reach his location, or the scripted end of the battle won't trigger.
 * In Red Dead Redemption, you can get into Nuevo Paraiso and West Elizabeth well before you should be able to. The initial methods, which have since been patched, were camping on the New Austin side of the middle bridge to Nuevo Paraiso and camping on a very specific spot on the New Austin side of the river dividing New Austin and West Elizabeth to get into West Elizabeth. After they were patched, people found you could still get to West Elizabeth by getting arrested by the police in a spot that the game considered part of West Elizabeth but was actually in New Austin. After THAT was patched, people found out yet another way of getting into West Elizabeth; by riding a stagecoach down the hill near the broken bridge leading into West Elizabeth and aiming for the river, you could sail across to the other side. And people found out that it was then still possible to get over to Nuevo Paraiso by standing on the very edge of the aforementioned bridge to Nuevo Paraiso, shooting anyone you could see in Nuevo Parasio to rack up a bounty in Nuevo Parasio and then racking up enough for the police to get close enough to arrest you and take you into Mexico. There's not much to do besides buying properties and doing challenges, though.
 * During the hospital escape sequence in Max Payne 2, there are a couple occasions where hospital security is gunned down by the cleaners before the player can, theoretically, take action, but if through cheating or just sheer skill the cleaners are killed before they can shoot, the hospital security will just drop dead where they're standing anyway.
 * An odd and semi-famous example: in Call of Duty: Modern Warfare, if the player turns on an infinite ammo cheat and scores a direct hit on the Hind that's chasing the truck (something that's impossible to do in normal gameplay), the ending changes. During the final scene where Zakhaev appears, a friendly NPC inexplicably gets off the ground and kills all three of the Ultranationalist soldiers with melee attacks before standing around as the Loyalist helicopter blows up the Hind behind him. Depending on when this occurs, Gaz will sit up and fall back down (even though he wasn't shot in the head), and when Soap receives the gun, there are no enemy targets to fire at - Soap puts the weapon down a few seconds later.
 * In Call Of Duty: World At War, on the Vendetta mission, by performing a series of very simple jumps after the sniper duel, you can reach the area where Amsel is later on in the mission. There are invisible triggers all over the place which spawn soldiers, trucks and Amsel. By going through the triggers in a certain order, you can get Amsel to appear. This makes getting the achievement for killing him with a pistol a LOT easier.
 * A minor-but-amusing case in Final Fantasy V. Normally, the first time you enter the Sealed Castle in the second world, Galuf will explain to you exactly what the Castle is all about. It is never required that you visit the Sealed Castle in the second world, and if you put it off until, then
 * In Fire Emblem the Sacred Stones, you can instigate some support conversations that refer to characters that haven't joined. Notably Neimi will refer to scaring Cormag with her stare, even if Cormag hasn't joined your group (And is still a soldier of the enemy, and thus wouldn't even be known by Neimi.)