Paperboy, the coin-op version, had a race where you tried to get through a timed game. At the end of the race, you're supposed to cross the finish line. Here's where the bug comes in: if you cross just off the edge of the finish line outside of the edge but before the hedge of the game, it switches to an inverted video version of the race you just ran. This game normally has a high score of around 50,000, but the scores for things you hit in this strange area are way out of range, making it possible to get a score of around a billion, so high it can overwrite part of the screen.
Castle Crashers had a glitch that would cause the boomerang to get stuck on any three bosses if the boss was between you and it. Since experience points are given based on how much you hit an enemy and not how much damage you deal, and the boomerang does 1HP damage per hit, the stuck boomerang would rack up hits and increase your experience quickly. A patch fixed this, but replaced it with a completely different Good Bad Bug that made the Boomerang able to demolish any destructible barrier in one throw.
The video game adaptation of Spider-Man 2 allows you to fly into the stratosphere if you're hit by the train.
In New Rally X (or at least the Xbox Live Arcade version), a glitch can cause you to go onto the walls. This can sometimes end up saving you, as the CPU-controlled cars can't get you there.
Bayonetta has a rocket launcher, which is very powerful but slow firing. The bug is exploited by putting her claw weapon in lightning mode on her feet in the first weapon set and the rocket launcher on the second. Then just use the rapid-fire kick attack of the lightning claw and switch weapons after the animation starts. Bayonetta will continue to do the claw kick animation and fire the rocket launcher with every kick for massive damage.
DmC Devil May Cry has multiple glitches that make Dante fly around the screen avoiding enemy attacks, bosses that are unwilling to attack or are just paralyzed. The fandom decided to use them to have fun.
In Sherlock Holmes Nemesis, the player, as Holmes, must have his companion Watson with him, of course. Unfortunately (or hilariously), instead of simply having Watson walk behind you, the game engine never has him actually move. Instead, he simply appears to soundlessly teleport right back next to you whenever you're not looking. A hilarious YouTube video illustrates the problem.
Infocom games, being text-based, have some of the most amusing glitches in gaming, as your mind can fill in ridiculous blanks to make them seem more ridiculous. Some gems include poking the idiot in Arthur: Quest for Excalibur, causing him to drop dead and losing you the game, giving robotic commands, even suicidal ones, to the humans trying to kill you in Suspended, and throwing body parts, like your hands or head, across the room in Plundered Hearts, leaving them lying there on the ground where you can't retrieve them.
Sherlock, the followup to Melbourne House's already infamously-buggy Hobbit, was less a game and more a collection of wonderful errors strung together with plot. Contemporary videogame magazines had a cottage industry of finding the best bugs, giving us such gems as:
You can see an unconscious policeman. An unconscious policeman says " I'm sorry, sir, I have my orders, but no one is to get by. "
Card Battle Games
The Special Digivolve card in Digimon Card Battle is supposed to allow you to digivolve your current card into a Digimon of a different specialty, adding 20 DP to the amount required for digivolution in exchange. That's how it's supposed to work. Instead, using the Special Digivolve card actually reduces the amount of DP required by 20. In addition, if used on a Champion-stage card whose stats are halved because it wasn't digivolved from a Rookie, Special Digivolve results in an Ultimate Digimon with full stats.
However, the manual states that this is a feature, not a glitch.
In Yu-Gi-Oh! GX: Spirit Caller, the pack glitch. Apparently, whoever was responsible for the code for buying packs en masse did a horrible job of it; there's a fairly easy way to buy all or all but one of the packs in a set for the price of a single pack. This can potentially mean that you're buying 51 packs for the price of one.
In Yu-Gi-Oh! GX: Duel Academy, it was possible to give the Copycat monster an obscene amount of Attack points. At least one AI duelist (in this case, Blair) uses Scapegoat, which creates a group of tokens on the field. Bringing out Copycat and having it copy one of those tokens would, strangely, give it more than 30,000 points when it came time to attack. Note, however, that the exact circumstances that lead to the Attack increase are not known, so use with caution.
Burst Stream of Destruction should only be playable if you have a Blue Eyes White Dragon on the field, but the game doesn't check for it, so you got a unrestricted card (i.e. you can have 3 of them) that can destroy all monsters on the enemy field and is also fairly easy to get.
Pokémon Puzzle League has a habit of freezing either player during a 3D puzzle match. This is one of those cases where the bug is both a Game-Breaking Bug and a Good Bad Bug, as depending on which player is frozen, you'll either have to restart the game or just wait for an easy victory.
Tetris DX's rotation system is such that your current piece, provided it isn't the square "O" piece, can be kicked back up the wall, over and over, so that the game never actually progresses.
The physics engine in Scribblenauts is decidedly fickle, and known for producing its fair share of bizarre (and hilarious) spazz-outs. Just for starters, objects made with lots of other objects (e.g., sticking together with glue) have a tendency to "creep" along the ground with steady momentum. Sticking too many things onto something Maxwell can pick up (like a BASEBALL BAT) can result in him being flung across the screen when the creation explodes.
Also, using the "Shrink Ray" on summonable terrain features like the "Hole" creates gaps that it's possible to escape the stage through.
Terrain features containing water (like the "Sea") can buoy floating objects in themselves without being placed down. This can even be used to carry Starites in things such as ice blocks to you!
Summoning items that always vanish upon being put into the world (like "Bubble") in the level editor results in said item not vanishing, and becoming a lovely fountain of its appropriate particles. If you start the level you've created, they'll stick around, and you can knock them about. Not surprisingly, though, the huge particle streams crash the game rather quickly if you start summoning other things.
Similar to glue, rope and related objects can create numerous glitches. You can instantly win almost any level by spawning a container next to the starite, attaching a rope to the starite, and then attaching the other end of the rope to the container, which allows you to put the rope and starite inside the container and drag the container all the way to Maxwell instantly.
Another rope-related glitch is the classification of attached objects as one object. Basically, if you attach two objects together via rope, they can pass through each other, meaning that you can attach a starite to a gate and then have it fall through to the other side of the gate.
Attaching an object that causes other objects to gain momentum with one of those items using a rigid body (like glue and planks) yields hilarious results
This includes the "flying bridge" glitch, where using a fishing rod on a bridge Maxwell is standing on causes him to fly to the ceiling or off the screen, where he dies.
Some animals, like gorillas, can both ride things and be ridden on, allowing you to easily create things like gorilla totem poles that slow the game down to a crawl.
Scribblenauts Remix has a silly glitch in which making a building ridable can allow the player to walk offstage or even clip through the ground.
In Supaplex, there are numerous small glitches to avoid getting killed in some occasions and how to manipulate with enemies and explosions. These have found various uses in many of the custom levels.
Blast Corps had the Z-Button trick. When in a vehicle, if you are in the right spot next to a building, you could hold the Z-Button down and wait for the doh! sound to go away, which was the cue that meant your character got out of the vehicle and, in the process, destroyed whatever building the vehicle was next to at the time.
Puzzle PlatformerThe Castles Of Doctor Creep had a couple of doors in the castle Doublecross that didn't go where they were supposed to. The effect of these doors was to basically create two shortcuts that considerably shortened the castle.
The DDR Extreme arcade cabinet had a difficult-to-time trick in Oni mode. When switching between courses, the song list shuffled off the screen and is replaced by the new one. By pressing the start button in the middle of this animation, the cabinet may accidentally load the correct songs for the course, but load the difficulties from the previous one. Most combinations don't produce anything special—either a crash and reboot of the machine or Heavy step charts mislabeled as Challenge—but a few courses reveal Challenge-difficulty step charts that were Dummied Out and are not playable through any legitimate means.
Due to the way DJMAX Technika's touch screen handles touches, you can do tap notes by dragging your finger across them, and conversely, you can do chain notes by individually tapping each individual segment. Whether this is a legitimate way of playing the game is a matter of debate.
StepMania 3.9 (and "3.95", the version used by In The Groove 2) has a series of bugs that allow for some serious Interface Screw. The most famous one is perhaps the "Negative BPM" bug, which can be used to create warps, which can then be used for a wide variety of effects and tricks. It has been leveraged to create crazy fan favorites.
Unfortunately, this bug was fixed on 4.0. However, sm-ssc (StepMania 5) turns it into an Ascended Glitch by providing built-in means to perform warps.
Rock Band 3, on PS3 at least: some venues have large props that the rockers sometimes stand on. There's one venue with lots of green lanterns that does not seem to have such a prop, but the game seems to think it does, so rockers will sometimes stand several feet above the stage.
In the original Space Invaders, the "random" point value of the flying saucer was actually a completely predictable function of how many time the player had fired. It was worth 50 points if hit with one of the first 8 shots, 100 points if hit with shots 9 10 11 or 12, 150 points if hit with shots 13 or 14, and 300 points if hit with shot 15; then the cycle started over. A savvy player could count his shots and get 300 points each time.
A far more overreaching one; when the game was originally designed, the amount of sprites on the screen seriously lagged the system. But by shooting them, and hence removing those sprites from the screen, the system sped up, so the Invaders did too. This mistake introduced Turns Red to the industry at large, and while other games like Break Out did it first, it popularized the entire concept of Difficulty By Acceleration.
Sinistar had a bug that allowed you to acquire 255 ships. It takes a second or two for the Sinistar to eat your ship, during which a Warrior ship can shoot you, making you lose two lives at once. If you started with one life, your number of lives would drop from 1 to 0 to -1. Since this number was stored as an 8-bit unsigned integer, -1 would register as 255.
Later games in the Touhou series have Marisa's B firing mode glitched up. In Mountain of Faith and Subterranean Animism, using Marisa B with 3-3.95 Power caused insane damage, enough to cut lengthy cards to a third of the length. It's a bit nerfed in SA, though, as you need to shotgun with a specific formation. It also fails in MoF if the player focuses.
And akin to this, "Malice Cannon" in Imperishable Night. As the Magician Team (Marisa and Alice), repeatedly tapping the focus button allows both characters' attacks to be used simultaneously. This bug doesn't break the game, but rather moves the ridiculously underpowered Marisa/Alice team closer to the damage output of the other teams.
The Malice Cannon actually buffs up the Magic Team to the strongest team in the game, with a ridiculous damage output, although the player still has to deal with the fact that it only fires in front of them. Technically, all four teams have the ability to perform this bug, however, the Malice Cannon is the most notable, because Alice's attack is a narrow laser that reaches across the whole screen in basically the same instant it's deployed, the Malice Cannon can deal consistent damage, instead of waiting for both teammates' bullets to reach the enemy.
Lunasa from Perfect Cherry Blossom can glitch at times, making her "Fake Strings 'Pseudo-Stradivarius'" card last unusually little for Reimu A, should you choose to fight Lunasa after the sisters' first joint attack. While the glitch can be observed with a certain degree of consistency during Normal and Lunatic gameplay, it's currently unknown whether or not it can trigger on Hard, given that the script for "Spirit Strings 'Stradivarius'" is noticeably different on this particular difficulty. The glitch, nonetheless, trivializes the card, which comes to ease the heavy-dodging you're normally subject to with Lunasa. you can watch the glitch on action here (skip to 5:53).
In Ten Desires, due to a glitch in the way Mamizou's creature bullets are animated, the script that tells the game that a bullet has already been grazed doesn't activate. What this means is that by simply sticking close to any creature bullet, the player can accumulate ridiculous amounts of graze, far more than the actual number of grazed bullets. While all of Mamizou's cards feature this to some extent, it's most noticeable during Wild Deserted Island, which fills the whole screen with nothing but creature bullets.
Almost all spellcards in Touhou gradually reduce the points you get for capturing them over time, so capturing a card after 15 seconds gives more of a reward than capturing it after 20 seconds. While this is normal and fine in itself, it can lead to some odd quirks in a few cases; for example, Yuugi's first boss spellcard on Lunatic has a rather low reward for capture. If you spend enough time against the spellcard, the capture bonus will go negative, causing you to actually lose points for capturing it. Then there's Rorschach in Danmaku, where the point value fails to change at all; if you time it out, the game will consider it a capture, as shown here...though given that this card is That One Attack, scorerunners generally do not appreciate this fact.
In the later games with spellcard practice (as of this writing, Ten Deisres and Double Dealing Character) you can practice any spell you've seen with any character. This is intentional. What isn't, though, is that doing this unlocks the relevant stage practice, even if the card in question isn't even in that character's version of the stage.
Suwako Moriya's first spellcard in the Extra Stage of Mountain of Faith has a glitch wherein the laser waves that is normally intended to fire downwards will fire on the direction the player was positioned during the pre-boss conversation. The player can cheese the spellcard by positioning himself above the screen on the center before the pre-boss conversation take place. This results with the player only has to dodge the homing bullet bursts without having to contend with the enclosing waves of lasers.
Older Than the NES. In the Combat game packed in with the original Atari 2600, running your tank into the inside of a corner—usually a corner of the screen—would teleport you to the opposite side.
In Tank Pong, after one player successfully kills the other and his tank is still in motion during the "death sequence" (i.e. the "dead" opponent spinning), if the victor's moving tank touches the wall bounding the playfield, his tank will suddenly start sliding rapidly along the wall, warping around off the edge of the screen and back out the opposite edge, until the next round begins. If the same victor's tank touches the beaten tank while doing so, he also takes the spinning tank with him in that joyride.
In any Tank game, having both players' tanks positioned one right in front of the other (i.e. one Tank's gun right on the other's rear) and touching, and having both move forward, will cause both to suddenly begin spinning rapidly in a circle (and passing through any nearby wall or barrier).
In Afterburner Climax, after lighting the afterburners for a while they would automatically turn off and your plane would slow down to cruising speed. By deliberately throttling back from the standard middle position and then shoving the throttle forward again periodically, you could maintain afterburner near-continuously. This was not removed from the XBLA and PSN releases.
In the original Escape Velocity, one could suppress planetary defense fleets entirely by hiring enough escorts to achieve the cap on the number of ships in a system.
Metal Gear Solid had the Instant Elevator bug. Rather than wait after calling an elevator, if you hit the button again it would arrive instantly.
It also has the Vent Glitch used by speedrunners. Switching to first person view while in a specific position in a specific vent causes Snake to go out of bounds. Guiding him then to certain spot causes a cutscene to be triggered that advances the story to the part where Snake has been captured, allowing him to skip 5 bosses, at the cost of having a shorter lifebar.
There is also this rather difficult to explain glitch that allows you to get up close and personal to Sniper Wolf in both battles. Normally if you try to get too close you are automatically hit by a scripted unavoidable attack that blocks your progress but through a specific glitch involving a grenade and a ration you can render yourself immune to it, run right up, and punch her to death as she helplessly strafes around still trying to snipe you.
Third Person Shooter Games
Saints Row 2 has a slight glitch having to do with reloading. Usually, your nameless protagonist will reload dual SMGs by spinning them in his/her hands and keeping them at his sides. Sometimes holding down the button makes the game act as if you are still firing while you are still in a reloading animation. Meaning it looks like the guy you took out in front of you was killed by some crazy richochet.
Go at a high speed and ram a gas station pump. You'll blast off farther than the Team Rocket trio.
Saints Row: The Third has a bug where, on occasion, the D4TH Blossom SMG just fires from its total ammunition without the Boss having to bother with replacing magazines.
Mafia has several. For instance, while the civilian population's driving AI usually works fine, it sometimes fails amusingly, leading to 'drunk drivers' barely managing to stay on the road and eventually crashing into obstacles. Also, try getting out of e.g. a racing car and stealing a car from gangsters. They will in turn get into your abandoned car, pursue you with it, and die horribly as their AI can't cope with a car that fast.
Another incredibly useful exploit: Reload your weapon and immediately perform a sideways roll to have your weapon be instantly-reloaded without having to wait for the reload animation to complete.
And Resident Evil 4. Unfortunately you could only dodge when you're being attacked, and most enemies don't give you enough of a warning to use this bug reliably.
Gears of War final boss General Raam is extremely difficult for two reasons, his handheld minigun and his shield of kryll bats. Mercifully, it is possible to trick him into standing behind the last cement block to the right of the platform where he appears, where he stops moving and does not target you with his gun as long as you don't stick your head up from cover. Getting him into this glitch spot is tricky and the other sources of damage can still get you on insane level, but this trick is enough to bring down an impossible fight to an almost manageable one.
Kid Icarus: Uprising has the infamous Play Dead+Jump glide combo. Basically, one of the powers you can equip is Play Dead, which, when used, causes your death animation to play (A Smash Brothers style explosion and a gravestone popping out where you were). The intended use doesn't really work because the actual death animation also involves being knocked back several feet into the air and the gravestone lasting for more than just a second. It also doesn't work as well as a get away tactic because your invisibility goes away almost immediately once you start moving around. It's used more for the fact that you are invisible AND invincible when you use it, making it great for sniping since you won't be moving around much anyway. The bug comes when used with Jump Glide: That power launches you into the air and lets you control your trajectory as you slowly descend. The game doesn't count this as moving and as a result, doesn't de-activate the invincible "dead" state, letting you use the power for more than just sniping weapons, and even with sniping weapons it allows you to change your position, especially useful if someone saw you play dead and was sticking around to destroy you once you "respawn".
There was an online Martian Rover Sim in 3D, which had been designed as part of the mission's publicity. The Sim was designed to show how the rover would move and collect samples. It also had some speed settings which, instead of speeding up the whole animation, increased the speed of the rover, allowing some really stupid stunts. You could take the rover to the edge of the map, where there was a small wall, climb it, and head out into the wide red yonder, which caused the rover to drive upside down through the air, among other things... Not bad for an educational resource!
Microsoft Sam has a very interesting way of saying "soi" and "soy". This sound has come to be referred to by some as the ROFLcopter.
In the Google Earth flight simulator, if you hit the ground, you die. However, if you start on the ground, don't take off and be very careful with the controls, the game doesn't register you hitting the ground as dying. Because of this, you can, among other things, taxi a propeller plane through/out of/into the Grand Canyon/Mount Everest and taxi a F16 on/under water.
The still-alpha Windows-clone ReactOS got a bug in its hard disk driver that caused it not to register and prevent access to disks - or it would have, had the Plug-n-Play infrastructure not been so screwed up that it set everything up anyway.
In Magic: The Gathering, the stack operates in a "Last In, First Out" manner. This means that the last ability put into the stack, played in response to something, occurs first. This can be exploited whenever something has a "leaves play" effect and some other effect. Often, these "leaves play" effects undo the previous effect, but if you somehow remove the card from play in response to its other effect, the card will leave play without undoing anything, and then the initial effect activates and never gets undone. This can remove lands, creatures, cards from a player's hand, and life permanently. If you remove the exploitable card from play by returning it to your hand, you can even repeat the effect!
"Patched" with recent versions of those same cards that are worded so that that trick doesn't work anymorenote The new cards set up a static ability with a duration rather than a delayed trigger. If the end of the duration happens before the beginning, i.e. the card leaves play before exiling the other, the effect never occurs. You might be able to get away with it in friendly games if you use the older cards, but tournament rules always go by the current wording.
deviantART had a bug that if you checked a message as soon as you received it, the time would sometimes say, "In the future."
The explanation may be more mundane. A lot of web frameworks have reusable functions to convert dates into human-readable relative descriptions, such as "5 minutes ago" or "1 day ago". They're written to be usable for any date in the past or the future: so, for example, you could have reminders that activated "in 2 days" or "in 30 minutes".
Certain more recent Tamagotchi models have a trick with a pencil and a screwdriver that lets you access the device's debug menu, which allows you to choose any pet you want, including those that were Dummied Out.
YouTube had a bug where if you put a 0.1 second pause at the end of a video, it will sometimes loop back to the start. This led to some interesting results. Sadly it doesn't work anymore.
Speaking of YouTube, the official iPhone and Android apps for the site both have exploits that allow you to view 18+ videos without an account. They also have exploits that allowed private videos to be viewed by anyone, such as when Team Fortress 2's "Meet the Spy" video was leaked a few hours earlier than its intended release.
YouTube has a hilariouslybroken auto-caption transcribing system that never fails to completely mangle whatever you ask it to add subtitles to. Most of the problem seems to come from the fact that the system tries to translate every sound it hears into dialogue, which then becomes a complete mess. It has provided numerous hilarious captions and even one case of Ascended Fanon in the My Little Pony: Friendship Is Magic series. note A one off-character was named "Steven Magnet the Sea Serpent" in a toy line after the fandom gave the name to the as-yet unnamed character thanks to one of these translation screw-ups.
Family Feud on the SNES was very buggy in terms of what it would accept as the correct answer. The game usually just checks if the first few letters of your answer matches any answer on the board or if they're in the same order regardless of what other letters are between them, so sometimes entering gibberish, swear words, or just about anything else could match something on the board even if your typed response is way off the mark. Milked for all it's worth in this TAS, and discovered hilariously in this Game Grumpsclip.
In Grand Theft Auto, pressing the horn button while on foot would make the player character fart and belch. This action can still be done if the player is killed.
Someone on Facebook discovered the Thai ideogram ส็็็็็็็็็็็็็็็็็็็็็็็็็ does a neat format-breaking trick, so it spread quickly.
Similarly, someone realized that you could abuse combining marks in Unicode to make characters stack and overlap. Th̢i̢s ̢uńlea͞s̨he͏d̛ t̕he ͞ni̡ghtma͟ri͡s҉h́ Zalgo ùpon̕ t̕he w̶o҉r͏l̢d.̀ H̵̕͜͟͝e̢҉ ̛͏̴̕c͘͢ò́͜͢͞m҉̢̛́é̸͟͝s͡.̵͢͞҉͢.̵̀͘.̵̀͢͞͞
In Vampire: The Requiem, there's an in-universe Good Bad Bug with the third tier of the Coil of Blood (which causes a vampire to receive three points of Vitae for every two Vitae they actually drink). The bug is when two vampires who know it use it on each other, allowing them to harvest theoretically infinite amounts of Vitae. It's well-known and generally banned due to the almost inevitable consequences of the ensuing Vinculum.
One online Pokémon battle simulator will sometimes get stuck on processing a move in a battle against an NPC, forcing the player to refresh the screen and turning back the clock to the last action taken by the player. Very helpful if the last thing the NPC did was knock your Pokémon out.
In-story example: Wreck-It Ralph features Sugar Rush, featuring Vanellope von Schweetz as a "glitch". She's barred from appearing in the game for fear that her presence will cause their game to be decommissioned. When she finally appears, she's the most popular character as players exploit her quasi-random teleportation to get an edge in races.
In-story example: Snow Crash describes a bug in the Metaverse which Hiro exploits to move through walls.
In the TRS-80 game Starfighter, pressing a number key 0-7 accelerates you to a pre-selected speed of 2^(number) - 1. Thus, pressing 3 accelerates you to speed 7, pressing 4 accelerates you to speed 15, etc.. It didn't take the players long to discover that if you pressed two number keys at the same time, you'd accelerate to an intermediate velocity — and that holding down all the number keys 0 through 7 at the same time would accelerate you to speed 254, faster than any spacecraft you'd ever encounter.
"Under no circumstances can any [Necron] make more than one teleport move in a single turn. There are no exceptions to this, no matter how clever your logic."
In Games Workshop's The Lord of the Rings tabletop game had a rule that stated "Frodo counts as a banner in all respects". A later reprint of the rulebook added "with the exception that he cannot be picked up and wielded by another model". Oh, the mental images.
In Bar Rescue, one of the bars that the show went to somehow managed to drop a grilled cheese sandwich into a fryer. The resulting fried grilled cheese sandwich was enjoyed by the host of the show and the staff of the bar, who then put it on the menu.
A good amount of games that has developed these Good Bad Bugs, have gotten good to the point that they are seen as part of the game, sometimes becoming an Ascended Glitch. Some of those bugs go from Wall-Bouncing from Gears of War, to canceling the reload animation in some games, and crouch-jumping. Some of these have become so well integrated with the game that they are seen as part of the game and sometimes crucial, to the point that they are allowed at tournaments and official games.
The robot used for Google Street View images was programmed to recognize human faces and blur them out. Amusingly, it sometimes can't tell actual faces from representations of them, so it will blur the faces of religious monuments, mascots, and other large statues.
Not really a bug or a glitch, but the Nintendo64 had a feature where if you press L+R+Start, it would reset the center point of the joystick. You could use this in some games to effectively enable an improvised cruise control.
Real Life Examples
The 1981 Cadillac El Dorado had a balancing problem which was corrected by installing a steel plate underneath the driver's seat. This saved Frank Lawrence "Lefty" Rosenthal from a car bomb attempt, which served as the inspiration for a scene in Casino.
Electronic novelty items that speak or sing while moving a part of them, such as singing fish. The fact that a fish on a plaque is flapping its tail to the music and lipsyncing is funny enough as it is to many people, but let the batteries get low and they get slowed and off-keyed when they try to move themselves. The effect is pretty funny.
Some synthesizers, like the Hing Hon EK-001, can sound like they're dying if they're low on batteries, too.
This happens with the old edutainment toy Speak n' Spell, but that's a Bad Bad Bug.
The Simon memory game would actually run faster (and its notes would play higher) if the batteries started to get weak, making for a more difficult challenge. However when the batteries were really weak, the device would no longer work properly and would simply become a light show.
Genetic mutations. They make species evolve into having useful new traits and create wild new species... occasionally. The rest of the time, they simply cause cancer and a variety of other awful conditions.
The sickle cell trait causes a defect in some of the carrier's red blood cells, making them deficient at carrying oxygen. This coincidentally means that malaria parasites can't grow inside them.
The Cowpox virus. Being affected by this benign disease makes one immune to the far deadlier smallpox. This observation and subsequent successful use of a preventive treatment against smallpox forms the basis of vaccination medical therapy.
Will Keith Kellogg and his brother, John Harvey Kellogg, of Battle Creek Michigan, were Seventh-Day Adventists and ran the Battle Creek Sanitarium in the late 19th century; the food, in accordance with their beliefs, was to be served bland. One day, they had to leave some wheatmeal sitting to take care of a problem at the Sanitarium and came back to find it went stale. Since they had to keep a tight budget, they couldn't just throw it away, so they decided to roll the stale wheatmeal to make long sheets of dough. They were, however, surprised when the wheatmeal instead broke off into flakes, which they baked and served to the patients. It turned out to be very popular breakfast food with the patients, so they decided to play around with the recipe by substituting other grains for wheat. They struck gold with cornmeal and went into the breakfast cereal business, and the rest, as they say, is history.
The Winchester 1897's external hammer meant it lacked a trigger disconnector, which was never considered a problem as the gun operated as intended. However, this meant that you could fire the shotgun simply by holding the trigger down and pumping the action, a phenomenon known as "slam firing". This essentially meant that its rate of fire depended on how fast you could pump. Dangerous at a shooting range, lifesaving in the trench warfare of World War I. At least, if you weren't on the receiving end.
This was such a horrific thing to be on the receiving end of that Germany actually accused the United States of human rights violations for using the shotguns to clear trenches, citing the part of the Geneva Convention restricting the use of cruel and unnecessarily painful weapons. Note that, in the trenches, your one other option was a trench knife that would undoubtedly cause a festering wound in a war zone. Compared to that, the shotgun was downright humane.
Quantum tunnelling. There's a finite probability that something thought impossible in classical physics, like an electron moving through an insulator, can happen. It's because of this that flash memory and electron microscopes work. And the Sun keeps shining for that matter.
The TRS-80 color computer, back in the 1980s, had a glitch where the computer did not know if it had already written color to a pixel. This flaw allowed a far greater color pallete because multiple color instructions could be written to the same pixel, which then displayed much the same as blending colors on an artist's pallete.
For the final mission of Ace Combat 5: The Unsung War there is scripted speech that lasts around a minute. With the right place and weapon the fight can end in five seconds, with the game not being able to keep up because you are just that good. That's not the good part of this bug however, the good part is there is another lengthy scripted sequence that can be interrupted, you can hear it all if you're good enough beforehand or just cheese the fight which gives more than enough time for the scene to play out.
Gary Gygax bought a bag of cheap plastic toy dinosaurs to use as miniatures in the new fantasy-based tabletop war game he and his friends were messing around with. Several were so badly-crafted that they not only didn't look like dinosaurs, but they didn't look like anything that could possibly exist in the real world. Rather than throw them out, Gygax made up names and abilities for the glitch-marred toys, ultimately adding three iconic monsters — the bulette, owlbear, and rust monster — to the Dungeons & Dragons game.
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