Darksiders has a glitch in the Ashlands area. Outside of one of the pits is a trio of horse-riding demons. If you jump into the pit and crawl back out of it, a trio of riders will respawn regardless of whether or not you killed the former ones. You can do this enough times to completely fill the area with riders to the point of being able to crash the game. Some gamers like to exploit this bug in order to quickly gain souls and sword experience.
Batman: Arkham Asylum and Batman: Arkham City have an absolutely hilarious glitch with the ground takedowns. Rather than crouch on the poor mook's chest and hit them in the head, occasionally, Batman will crouch on their head and give them a ball-busting punch in the nuts. An even rarer version has them flipped over as well, leading to Batman punching a man in the ass so hard he's knocked out. And an extremely rare one has him punch someone as a thug is getting up off of the ground, leading Batman to punch them up the ass hard enough they get sent flying.
Something similar happens with the Multi-Ground Takedown, as sometimes thugs get knocked across the street or into the air.
This gets a little weird when you're playing as Catwoman, because it looks like she knocks thugs out just by slapping their ass.
Perching on a billboard or on the fences that some building roofs have and facing the corner, and then rapidly shooting quickfire freeze grenades will have Batman slowly inch towards the edge, at which point, he'll start rising into the air. Go high enough, and you can escape the game boundaries and actually fly over the walls to explore the surprisingly detailed Gotham City (though there is no collision detection so you only get one glide) or across a vast expanse of water and actually reaching Arkham Asylum island, fully rendered (again with no collision detection) and then either falling through the floor and dying or falling into the water and having Batman use his Grapnel which apparently can reach across a lake back to one of the prison buildings.
The gnome glitch from the PC version of Harry Potter and the Chamber of Secrets, which let you create hundreds of gnomes in Moaning Myrtle's bathroom and send them running throughout Hogwarts.
The PS version had a really weird one: A bug in the game would let you warp directly from Ron's house to the Gryffindor Common Room way later in the game. However, you warped directly there without passing GO (or collecting 200 Every Flavour Beans, but anyways) which meant that other events in the game that should have been seen by now weren't, and when you go to where those events took place, you'd see those events - except out of order. One particular event that can be skipped "merges" with another event later, and the characters will spout random lines from both events. The game won't move on if you just let it sit in an endless loop like this so you have to keep pressing the square button and hope that you get out of glitched speech hell. Wow.
Back to the PC version, there's a point in Lockhart's spongify challenge where you have to fight three imps (which are like gnomes but faster and much more difficult) to move on. You can instead stay very close to the wall and prevent the platform from lifting and the imps from coming out in the first place, thus saving yourself time and aggravation.
Also in the PC version, It's possible to get an unlimited number of Every Flavor Beans in the greenhouse part when you collect potion ingredients. All you need to do is stand in front of a row of two flower pots, and cast at the the one behind the nearest to you. Continue casting, and beans will come out of it even after it's been knocked over.
The "Death Mountain Descent" glitch in The Legend of Zelda: A Link to the Past allowed Link to access areas in the Dark World that should be inaccessible until after you get the Moon Pearl, which counteracts that realm's Baleful Polymorph effect. Further glitches allowed Link to actually take human form intermittently and complete certain dungeons (but unfortunately not all of them). You can use this glitch to complete the game without getting the Master Sword, and/or follow up with other illogical things like refining your regular sword into the upgraded Master Sword.
By emulating or taking your controller apart, interesting things happen when you walk up stairs facing downwards by pressing u and Down at the same time. Interesting in that you go down a level instead of going up a level, letting you use room exits where there should be none, walking under the entire map of the game. If you use enter the Tri-Force room while doing this, the ending plays. This is how the game is speedrun in 3 minutes.
Another Zelda example is the warp glitch in The Legend of Zelda: Link's Awakening, which allowed many bizarre effects and Sequence Breaking glitches, similar to the Death Mountain glitch in ALttP. This glitch is so popular that many fans actually consider the colorized DX version to be inferior to the original solely because it fixes the glitch.
The glitch can unfortunately cause consequences if the player is not careful, like being stuck permanently with a companion that refuse to let you enter dungeons (the ghost Marin glitch), though it has some humorous effects, such as Moblins being replaced with the broom-sweeping old lady.
If you attempt to warp to the Face Dungeon (the sixth one) and save, there is no way to get out of it, even with the warp glitch.
In some versions, warping over the edge of the map while holding everything except the level 2 sword caused you to receive a glitched object, which replaced the original sword. You had to save and quit to exit the room with the object, and loading up the game, end up in Marin's house. If you didn’t corrupt the save file, you might end up with a buggy, extremely powerful sword, which could kill anything in one hit.
There is another glitch in Link's Awakening which works in both the original and color DX version, known as either the doghouse glitch or doghouse world. It is very easy to enter—just walk down the side of BowWow's doghouse and push left—and is perhaps one of the strangest glitches in any game. It consists of every dungeon room in the game jumbled up in a seemingly random fashion. The graphics are glitched all to hell, Link's movement physics are completely changed (he can usually walk through almost anything), and treasure chests will contain anything from a random text box from the game to items from high level dungeons, which are completely usable. This glitch is almost endless in its useful capabilities, but has never been fully explored.
While fighting Ganon, the number of bats he summons will almost overwhelm the graphic processor. You can push this over by throwing your boomerang, slowing down the action considerably and making the bats easier to dodge in a form of improvised Bullet Time.
Early copies of Ocarina of Time (predominantly those with a gold-colored cartridge) featured the "Swordless Link" glitch, which involved saving and quitting during the final battle right after Ganon knocks the Master Sword out of Link's hand. Doing so would put you back at the beginning of the final dungeon with no sword equipped. While this may sound lame, it was actually pretty cool - among other things, it let you use items while on your horse, leading to some interesting and glitchy gameplay scenarios (including being able to use the dungeon-only warp spell anywhere and catapulting yourself out of the game world into the nothingness beyond). It's even possible to do this in later editions of the game, but you need to use yet another glitch which allows you to play almost any item as an ocarina to warp out of the boss's lair with your sword unequipped.
Another Ocarina of Time example involved the Gold Skulltulas. One particular Skulltula was in a small cavern. It was possible to kill this spider, use the boomerang to collect its token, then backflip onto the panel that warps you out of the cavern before the boomerang returned to you. This caused the token to be collected, but the Skulltula to return to life, allowing for infinite Skulltula tokens if used repeatedly.
And then there's the infamous "bottle bug" that allows players to replace any item with a bottled fairy. While the fairy in the bottle thus created can't automatically resurrect Link like the fairies in normal bottles can, and the item replaced is gone forever, this can still be quite useful for an emergency life boost in the more difficult sections of the game.
And many others, including skipping all Young Link dungeons by glitching through the Door of Time and skipping all Adult Link dungeons by using the reverse bottle adventure bug. These and many more can be found here http://tasvideos.org/ZeldaOcarinaOfTimeTricks.html and make for some impressive speedruns.
Some players have found interesting effects by physically interfering with the connection between cartridge and console. If the player slowly lifts up one side of the cartridge while simultaneously running into anything destructible by bombs, Link might pass through the rock/wall/whatever. This allows the player to get into Goron City via Lost Woods before getting the sword, thus giving complete (but useless) freedom.
It can also be used to get past anyone who's blocking your path—like the Kokiri child who blocks your way out of the woods, Mido who stands between you and the deku tree, etc.—allowing you to get to Zelda and beyond without ever obtaining a sword.
One major glitch in Ocarina is the ability to "Seam Walk" by very carefully walking straight lines up the seams where two pieces of terrain meet at a gradual angle. The easiest place to do this is in the Gerudo horse archery arena but its actual uses include standing next to Biggoron (and passing through him to climb to Death Mountain's peak) and "invading" the oddly water-filled Hyrule Castle. Oddly, this glitch was never fixed: notice that in The Legend of Zelda: Majora's Mask the glitch is still possible, as Nintendo simply replaced most angled seams with vertical ones.
In Ocarina of Time: Master Quest there's an easy-to-do glitch that allows you to get through the WaterTemple in under 5 minutes, without needing a single key or encountering a single enemy.
One of many glitches exploited in SpeedRuns is the "Super-slide", where you roll against something that would cause damage and put up the shield at just the right moment, causing Link to slide backward indefinitely and at tremendous speed. Entering Cut Scenes this way has interesting effects. For instance, approaching the Forest Temple the first time as an adult, Link spends the whole cut scene hiding behind his shield, even while playing the ocarina, and mostly doesn't even show up onscreen since he's unable to walk where he's scripted to. Entering the Final Battle this way prevents Link from losing the Master Sword, with the side effect that it temporarily exists in two places simultaneously: stuck in the ground and in Link's hands!
You can easily win the second horse race against Ingo by following him closely, but then stopping just before the stable at the back of the ranch. Turning to the right and then turning back makes Ingo disappear, so you can take your time getting to finish line.
Also in Twilight Princess, you could get to the City in the Sky early by transforming into a wolf into a crack under Kakariko Village to clip through it and warp the cannon to Lake Hylia. Since the game only checks for the last mirror shard, it allows you to skip a dungeon and a half. Unfortunately, the game will block all access to previous dungeons once you do the skip glitch, as the game discards all the old events because it thinks you already completed them.
Not to mention the "Twilight Hack", a result of a particularly "meta" Good Bad Bug. Smashing the stack via Epona's name (laymen's terms: the hack used a save that gave Epona a very, very long name that tricked the game into running code designed by the hackers) has allowed people to use the game to boot the Wii into a root-level command prompt and install homebrew software on it. It's not really a bug in the strictest sense, since (especially after the latest firmware updates, due to later hacking developments including — and focusing on — piracy) it can't be accessed without hacking, but its bizarrely beneficial repercussions make it worth mentioning here.
It only works in the second dungeon, and even then only in the places with magnet force pillars, but putting on the boots with the D-pad and then replacing them with any other item before you hit the magnetized surface allows you to move at normal speed on the ceiling. You can't use items or roll, and your hat becomes immune to gravity, but it makes some parts much faster (and quieter).
There's also the infinite-bombs-and-arrows glitch that can be done by exploiting the connection between Iza's Rapid Ride and Plumm's Fruit Pop Flight Challenge up Zora's River. By playing the latter beforehand, and using the clawshots while swimming to clip through a wall, you can purposely fall out of bounds in Lake Hylia. What makes this glitch possible is the fact that when the game respawns you, it returns you to the place you last entered the area— in this case, at the end of Plumm's game, which can usually only be played while you're a wolf— however because you died as human Link, you'll be respawned as human Link, in a situation that shouldn't be possible. After a few more deaths and respawns you can get so Wolf Link is playing Iza's game (another impossibility), but isn't in the boat. This allows you to warp out and when you turn human again, you'll still have the infinite bomb arrows assigned to your B button, as though you were still playing Iza's game. Having unlimited bombs and arrows makes the Cave of Ordeals a whole lot easier, among other uses.
Perhaps only possible in the GameCube version of Twilight Princess, pressing the reset button on the console at just the right moment after Link falls into Lava in the Goron Mines (sometime during the fade to black) causes Link to respawn normally, except in Hyrule Field. He can then run around, and you might notice the title music playing. The Title logo will eventually pop up, and pressing any button besides the control stick will cause the game to go into the file select screen.
It's also possible in the Wii version, although the timing must be very precise and it's harder to pull off. Also sometimes Link can spawn on a Bridge of Eldin; in that instance the glitch needs to be used again. If done correctly, the area which supposed to be Hyrule Field rendered behind the Title logo screen becomes fully explorable. This can lead to going outside the boundaries of the level, including going as far as the end of skybox, or watching the miniaturised textures of places which are in the distance, like Hyrule Castle. Oh, yeah. Epona is a MUST when going outside the walkable area, so prepare to see some flying horses.
In Majora's Mask, it's possible to wear the boss-only Fierce Deity's Mask virtually anywhere thanks to the glitch-filled Sakon's Hideout. Simply wear a mask during the second last section as Link, then when you swap to Kafei exchange that mask for the Fierce Deity's. The very first thing Link will do when you regain control of him will be to put on the mask he was "wearing" just moments before, and he will transform. Use that with a bug that lets you enter Sakon's Hideout on Day 2Day 1 and tell the Bomber Kid the password earlier on, and you can pretty much mess around anywhere you want for two full days with newfound superpowers. Just be careful not to talk to anyone whose lines varies based on which of the mask forms you're in — since the Fierce Deity is boss-only, those NPCs aren't programmed to properly react to it, causing the game to crash.
This glitch also leads to some other weird glitches. If you talk to some characters, they will react as though Link were not wearing a mask at all. Some react to him as though he were transformed, but they don't make a form-specific remark.
Also in Majora's Mask, you can keep looking through the telescope as the screen fades to black from running out of time. If you then press B to exit the telescope screen, the game does not end. All the time based events disappear and there is no timer.
The Use Restricted Items glitch in The Legend of Zelda: Ocarina of Time 3D. Not only does it allow you to use certain items and weapons in buildings and other areas, but to use Farore's Wind anywhere, letting you use any spot in the game as a checkpoint. It then gets better when you realise that you can use it to escape the final battle without a sword, accessing all known effects of the original Swordless Link gitch, or that you can break the camera system and activate a free camera in areas like the market and Temple of Time.
In The Legend of Zelda: The Wind Waker, there's the unlimited potions/soup glitch. Just press the button the item is assigned to and start at the same time, then switch it out for an empty bottle. Link still drinks the soup or potion, but it not only doesn't use up the stuff in the bottle but can even end up half filling the empty one as well. You can also use this to use items you're not supposed to use in certain areas, like bombs inside shops and houses and such like.
An interesting thing to note about using bombs inside buildings is that this can be used to blow up the delivery boxes inside Dragon Roost Island. They appear nowhere else in the game and this glitch is the only way to destroy them.
The main glitch used in speedruns of The Legend of Zelda: Skyward Sword is nicknamed Back In Time, and it involves dying, selecting Continue and resetting the game immediately afterwards: if done correctly, Link will still be controllable while the game is otherwise in the title screen. Depending on where and how it's performed, you can use it to skip large parts of the game by forcing the game to trigger cutscenes when it shouldn't, instantly warp to another save statue in Skyloft for a major shortcut and end up in partially-loaded dungeon rooms with missing obstacles that you can bypass earlier than you're supposed to.
In The Legend of Zelda: A Link Between Worlds, it's possible to skip the boss fight with Knucklemaster by using the Tornado Rod at a specific point. Done correctly, you'll end up in the area with the Skull Woods' Sage portrait. However, this means that you'll be missing a Heart Container.
In the Crusader games: drop an ammo-using gun. Pick it up. Its clip is now full. Ta-daaa!
Similarly, older versions of X-COM: UFO Defense will refill partial ammo clips that have been ejected from their weapons.
The first five Tomb Raider games have corner bugs, where jumping into a corner at the right angle makes the game think you are on top of it, causing you to warp to the top. This allows access to normally inaccessible areas, and therefore massively increases the amount of possible exploration in the games (as well as being helpful for things like Speedruns).
There's also the fence bug, which allows you to slip through gaps between fences. One notable use of this is at the start of the Obelisk Of Khamoon stage. If Lara is positioned just right, she can bug through the fence, allowing her to regain access to the previous level. See here.
The trigger bug is another useful one. Enemies appear when Lara steps on certain floor tiles. In some cases it is entirely possible to glitch past these tiles, preventing enemies from spawning.
In The Angel of Darkness, performing the level skip cheat and selecting the first level allowed Lara to climb down the ladder at the end of the stage without obtaining the gate key beforehand. By doing this, the cutscene to end the level is never triggered, allowing the player to explore a hidden training level which was removed from the official release. Despite being incomplete, it is interesting to note that the tutorial explains how to perform certain actions essential to the gameplay.
The ZX Spectrum game The Great Escape. You can give chocolate to a prisoner, who'll distract the guards in exchange for the bribe gift ... but you can also offer it to the stove, which will start moving around your room (to the same in-game effect). Also, unlocking a door improves your morale (which serves as the game's Life Meter); but nothing prevents you from repeatedly using the key on the door after it has been unlocked.
Little Big Adventure 2 has the famous "jump-save-bug", which allows players to jump to infinite heights by saving and loading the game in mid-jump. This allowed skipping large parts of the game and reaching places which are normally unreachable.
There was a glitch in Onimusha in which you could juggle an airborne enemy. This glitch was fixed before the game was released, but the testers thought it was so cool that they had to use it somewhere. Thus the combat system for Devil May Cry was born.
In Lego Star Wars on the Wii, there is a wonderful bug where any bonus activated will remain activated if you quit and load a different save slot.
Yume Nikki has a useful glitch that can boost your speed to the max RPG Maker 2000 speed (8x, if anyone's counting), making you amazingly fast. You just had to sit at your desk in the dream world, use an effect (using the bike effect made you even faster) and get off the chair. Especially useful for finding the rest of the effects!
Arguably an abstract Game Breaker, as Yume Nikki is designed to be a psychological sight-seeing game and isn't meant to be experienced at warp speed. Using the glitch, the player can easily and unwittingly breeze past the majority of the Easter Eggs and significant scenery in the game, making the experience something of a moot point. Definitely useful for those playing multiple times, though.
In Adventure, having too many items on screen would break the collision detection. This meant that sometimes your sword would not kill a dragon. It also meant you could phase through a dragon's body without getting hurt. Given that you would often be unarmed due to the one-item limit, and that you don't actually have to kill any of the dragons to beat the game, the good outweighed the bad. This bug is even mentioned in the manual. This bug was even exploited by the game's creator; without the bug, the game's Easter Egg wouldn't be possible.
The ancient Apple game Aztec (a side-scrolling Indiana Jones ripoff) had an AI that was less The Computer Is a Cheating Bastard and more The Computer Is a Sociopathic Monster. Fortunately, it was buggier than a Florida swamp. One of the best ways to escape a trap was to draw your machete and lunge forward over the boundary between rooms. Once you got to the halfway point, you'd fall to the next level and escape the trap. A related bug allowed the player to climb through the ceiling, walk up his own score and onto the floor of the room above. The crowner, though, was using a stick of dynamite at the beginning outside the tomb: it would bug the game into thinking you were on the 8th level, right near the idol, although with the caveat that you were now in the most hostile part of the tomb with no weapons or ammo.
In Kings Quest: Mask of Eternity, scaling a wall with the rope and hook in the Underground Realm of the Gnomes could result in Connor ending up on the other side of the walls bordering the level. Weirdly, it wasn't just an empty wasteland - there were rocks lying around that could be picked up and zombies to fight.
In Beyond Good and Evil, the ramp to the left of the item stand is particularly easy to clip through. While clipping through it usually leads to falling into the abyss, doing a forward roll and aiming properly lets you hit the warp space for a nearby door and get to one area earlier than you're supposed to. Using this to pick up an extra Plot Coupon earlier than you're supposed to allows you to buy an item that will get you past a Broken Bridge one dungeon too early. This causes tons of random dialogue glitches, total confusion on the part of your mission log, and, ultimately, a game freeze if you try to go to the next dungeon. Watching the game freak out is worth it, though.
In PAL version of Ico it's possible to use a glitch that allows Ico to jump a little higher than normal, and in some cases do really huge leaps. This allows for skipping large parts of game, including an entire wing of the castle. It works only in 50 Hz mode, though.
Legacy of the Wizard has the pause-jump bug, where pausing and unpausing the game will allow any character to jump again from mid-air. This makes it possible for some characters to reach areas they're not supposed to.
In the original version of La-Mulana the player could jump through the wall on the first floor of the Infinite Corridor and end up on the bottom floor, allowing the player to bypass an entire floor full of annoying block puzzles.
In Beyond Castle Wolfenstein it was possible, through judicious exiting and re-entering rooms, to actually "erase" Nazi guards from rooms. Given that wasting your time showing your pass everywhere slows you down when you need to leave the castle, this can be a time-saver.
In Star Fox Adventures, it is ra-- er, unlikely but possible, for the bat in one of the structures in DarkIce Mines to respawn in a wall and get stuck forever, or at least until you kill it or leave and come back. The respawn animation will loop forever, as well.
At Dragon Rock, pause the game while looking at the Earthwalker. His tail will disappear. After you free him, you can even look at him from the back with his tail gone.
Star Wars: The Force Unleashed had a brilliant bug where you could max out the level meter and gain permanent invulnerability and infinite force energy.
Because of the way Boktai 3 writes player-character's data to memory, it's possible to obtain Sabata's dark gun and Zero Shift spell through a carefully-timed reset. The gun itself is useless (the game crashes), but the dark lens is quite useful on some enemies and Zero Shift becomes a free and superior version of the Dash once you meet Cheyenne.