Tower Of Guessing Script Infinite Skips
First-Person Shooters BioShock: It is possible to play through BioShock without getting the Incinerate! plasmid. If you're very fast and lucky, you can hit a flaming trashcan downstairs and use it to melt the ice in the basement of the Medical Pavilion before it stops burning. The ice in Fountain Fisheries can be solved by telekinesising along a corpse with exploding buck, and then looting it after your weapons are confiscated.
In both games, any door with a combination lock can be unlocked at any time if you remember the code. This doesn't cut down on exploring as much as you'd think; you can't get the Lot 192 from Fontaine's apartment until you've visited Suchong's to find out what it's for, and the Fishbowl Diner is already on the way to Pauper's Drop. But the code to pass to the second half of Siren Alley in BioShock 2, which is also the easiest of all to remember, lets you bypass the Pink Pearl completely, including the boss fight with Daniel Wales.
It is revealed by Word of God this is why the Teleportation Plasmid was removed from the game.
The player is able to skip nearly the entirety of Blood's E3M3 by simply saving up jump boots from the previous map and using them to climb a ledge near the beginning of the map.
In Borderlands 2 you can, with some creativity, kill certain bosses before their introductory cutscene happens, as this video will show, but the game may take offense to your shenanigans if you do.
One of the easier ways to beat the Modern Warfare 2 spec ops level "Wetwork" is through a speed run where you throw flashbangs to disorient the enemy while you sprint past. When you reach the end, in the room where you need to breach the final room, the game will have reached its limit of enemies and so won't spawn any. As soon as you blow the door open, you win.
Most of the levels in Serious Sam - The First Encounter and The Second Encounter are out in the open. It's often possible to Rocket Jump over walls and triggers, leaving you with little to fight. In City of the Gods in Second Encounter, the player can even ram into one of the walls and fly to the exit of the level through interlevelic medium. Many of these glitches are very often used in multiplayer and it's not considered very entertaining by others.
The Doom II level Dead Simple requires you to kill every enemy to exit. One notable speedrunner (Drew "stx-Vile" DeVore) proved that you could use the rocket launcher to propel yourself onto the exit switch, meaning you could complete the level with 0 kills. In the original games, the player is unable to jump normally, and maps were designed with this in mind. Source ports that add jumping therefore allow you to skip large parts of multiple maps (in the case of the above Dead Simple, the entire map; same with Ballistyx, a TNT: Evilution map that's otherwise very long and challenging) just by jumping.
Similarly, any source port that adds vertical mouselook makes it possible to defeat the final boss in a matter of seconds, as the only thing making it difficult was the inability to aim vertically.
Some maps require you to find all three colored keys in sequence to open up the path to the exit, but in some of these cases, the obstacles you need the keys for are set up in such a way that you can walk past one of them without its key. MAP19: The Citadelnote where there are three colored bars, one for each key, blocking the exit, but the red bar in the center is twice as wide as the other two, meaning you only need the red key and one of the other two to pass through and MAP21: Nirvananote where the exit teleport is barred by two sets of key-locked walls; rather than one solid wall, though, they're broken up into two sections, with the outer blue one having enough space between them the player can simply slip past without grabbing the key are the biggest offenders.
Famously, the original Doom engine doesn't deal elegantly with heights and switch surfaces. In several levels, particularly mods, this can be abused by hitting switches way before you're meant to.
Various levels of Duke Nukem 3D can be defeated earlier than intended by exploiting glitches that allow you to, among other things, warp into rooms that overlap one another, crawl through spaces that are normally too small for anyone but a shrunken player to walk through, and pass through certain barriers. Even without using those, however, "Hotel Hell" (episode 3, level 8) can be completed just by throwing a Pipe Bomb through the crack at the beginning and setting it off, opening immediate access to the exit. (See this site for more information.) Also, generally the only levels designed with the jetpack in mind were the levels which contain a jetpack, not the levels after them. Though this isn't too bad, since there's only a few places in the game where you do get it (unless you use cheat codes), the jetpack in the hidden level from episode one can be used to skip the first half of the final level because it relies on a sequence of earthquake setpieces which each lower the terrain around the next trigger to somewhere you could reach on foot (and moreover on a lot of ledges overlooking the same area, so reaching any place you want is trivial). This may have been intentional, though, since it does require you to find and beat a secret penultimate level.
Also, many buttons can be pressed from the wrong side of a wall, and in many cases the mere act of jumping on top of an enemy can get one the boost needed to surpass the bulk of a level.
Halo has a lot of this (careful though, sequence breaking in the wrong place can render a mission Unwinnable): Halo: Combat Evolved has a major sequence break in the "Assault on the Control Room" level. In a stage about halfway through the level, one can get a Banshee fighter by knocking it off of a ledge with the rocket launcher. If you then fight through the following levels past the exit of the underground complex, you can then use the Banshee to fly up to the center column, where a new Banshee can be gotten to replace the (usually) now-damaged first one (even if you don't need it, you want to go get it to keep from being attacked by it as you pass and trigger that opponent). From there, you can fly over the following map sections to the one where you would normally have to proceed on foot underground; if you instead fly up to the overhead bridges, you can then enter at a much later part of the game, and because the triggers for the opponents have been bypassed, the following scenes will now be empty and you can simply proceed to the end on yet another Banshee that appears as you enter the last group of maps. In the remake, Halo: Combat Evolved: Anniversary, you get an achievement for stealing the Banshee.
This trick is also used to find the "Siege of Madrigal" Easter Egg music.
More Combat Evolved sequence breaks: It's possible to jump off the bridge in the latter part of "Assault on the Control Room" and onto the large buttress that runs up the front of the Forerunner shrine that houses the control room, allowing you to skip a decent chunk of the level. You can either walk down the bridge to where the mortar tanks and ghosts are, or walk up it and slide down the side to land yourself in front of the door to the control room.
From the self-same "Assault on the Control Room" bridge, you can also destroy the Covenant mortar-tanks below you, before you're forced to face them, from relative safety (it's very hard for them to get an angle on you: the bridge is in the way). You can eventually kill those mortar tanks by just shooting them repeatedly with small-arms, like the plasma pistols and rifles dropped by all the Covenant you just killed. * With a bit of practice, it's entirely possible to jump down from the very first bridge in Assault on the Control Room to the valley below. This will bypass the enemy spawn triggers and allow the player to saunter through the remaining 90% of the chapter unopposed.
Really, most of the on-line community for CE had at least some interest in and experience with sequence breaking (and pulling off stunts and pushing the game to its limits in general). It's likely that most experienced players spent at least some time on this, and it was probably one of the major sources of replay value in the game.
In Halo 2, Bungie cracked down on sequence breaking with instant-kill Invisible Walls, but there were many routes left open for sequence breakers: "Outskirts": The sniper alley and much of the courtyard battle could be bypassed by jumping from a little pile of rubble in an easily missed corner to a ledge, and from there to the roof-tops. Even better is that some players are good enough to hijack one of the Banshees and go flying over the level, in which you can find a giant soccer ball and a Scarab Gun.
"Delta Halo": The first battle, where you're supposed to neutralize the artillery, can be mostly bypassed without glitches or special tricks, although you don't get a Warthog if you do so, not that it matters much. There are also two spots in the mission where you can shortcut over hills that seem to be unclimbable, this allows you to skip the "Nothing But Jackal" sniper canyon.
"The Oracle": You can skip the Flood-o-vator ride by running around the small ledges on the sides of the shaft, although there is a death trigger that moves with the elevator, preventing you from doing it too soon.
"Metropolis": Take the Hog instead of the tank, it allows you to skip the Banshees and Wraiths during the bridge sequence. You can even squeeze the warthog through the tunnel into the sniper courtyard. Although it's better to switch to Sgt. Stacker's Gauss Hog there.
"The Great Journey": It's possible to get a Banshee into the final boss fight by squeezing it through the corridor leading to it, getting out at the right place and entering the boss' room, then going back and getting into it. This makes the final battle much easier, even on the highest difficulty. The same banshee trick is also possible by flying a banshee into a specific point on the building from the outside, which triggers the cutscene before the final boss and allows you to skip a few enemies before the final boss, and puts the banshee in the hallway before the boss after the cutscene is over.
Halo 3: ODST has skips in almost every single mission, though some are much harder than the others: "Tayari Plaza": You don't have to fight the pair of hunters that appear at the end; you can simply run past them through the very door that they spawn from. In fact, you can simply run past every single encounter in this mission, though it requires a lot of practice on Legendary to pick off dangerous enemies or disrupt packs of enemies with well placed grenades.
"Uplift Reserve": Not only can you easily speed past every single enemy in this mission, but you can also use boosted Ghosts to climb up some of the walls to take shortcuts. There is a reason this is often considered the single easiest mission in the entire franchise to complete on LASO.
"Kizingo Boulevard": There is a rather convoluted trick to steal a banshee and then fly it right up an invisible barrier, which you can use throughout the final firefight. It is also possible to push a scorpion tank into the final firefight area by using a second tank.
"Kikowani Station": There are ways to use banshees to break invisible barriers, allowing you to skip all of the doors that you normally need to unlock. You do not have to destroy the scarab at the end either, as you can just as well run past it.
"Data Hive": A rather tricky jump using fusion coils can launch the player onto the upper level of the drone hive, de-spawning all of the drones that would normally give you a run for your money.
"Coastal Highway": The invisible barriers outside the highway walls can be skipped by launching two warthogs past the wall and onto the ramp. Then the player can ride the second warthog out of bounds and carefully hit each and every one of the triggers, essentially bypassing the entire highway section and all of the vehicular combat involved. This exploit is known as Coastal Launch or Coastal OOB, and saves more than four full minutes in speedruns.