Unintended code with outsized consequences — beloved, infamous, and industry-changing
Clipping through the wall at the end of World 1-2 and entering a warp pipe before the Warp Zone has been set up sends Mario to a level the status bar shows as "World −1" — an underwater stage that loops forever and became one of gaming's most famous secrets.
Encountering the glitch Pokémon MissingNo corrupts the Hall of Fame records in Pokémon Red and Blue, scrambling the saved records of the player's championship teams.
Under certain conditions — most famously when it misses — Relm's Sketch command reads from the wrong part of memory, scrambling the inventory, equipment and character data and potentially corrupting the save file.
The Genesis version's hidden blood-restore code — entered on the "Code of Honor" screen to re-enable gore censored by default — became a flashpoint in the 1993 Congressional hearings on video game violence and a direct catalyst for the creation of the ESRB rating system.
A complete developer debug mode — allowing free flight, arbitrary object placement, and level data inspection — was left active in the shipped retail cartridge, becoming one of the most beloved and culturally significant oversights in 16-bit gaming.
Behind a door on the second level of Diablo's Cathedral waits the Butcher — a deliberate shock encounter, not a bug, that ambushes unprepared players with "Ahh, fresh meat!" and became one of gaming's most remembered scares.
A hidden character, Reptile, was programmed into Mortal Kombat's arcade version as a secret encounter triggered under near-impossible conditions — a deliberate "bug-like" secret that established the hidden content mythology the home console ports then amplified into a regulatory crisis.
Third-party map hacks that stripped away StarCraft's fog of war plagued public Battle.net play for years. Professional Korean play, held on supervised machines, was largely insulated; its gravest integrity crisis came instead from the 2010 match-fixing scandal.
A fundamental AI and aggro mechanic limitation in EverQuest allowed players to deliberately "train" large groups of enemies through populated dungeon areas, wiping out other players' groups — producing a years-long social and competitive crisis that shaped MMO design philosophy for a decade.
In GoldenEye 007's multiplayer, the short character Oddjob was so much harder to hit than the rest of the cast that "No Oddjob" became one of the most widely observed house rules in console gaming.
MissingNo — a garbled sprite representing a missing or invalid Pokémon data entry — became one of gaming's most beloved bugs by appearing as a catchable wild Pokémon through the Old Man glitch, duplicating items, and spawning an enormous mythology around its nature and origins.
A fundamental synchronisation problem between client-side prediction and server authority in early QuakeWorld network code produced visible "warping" of other players' positions, prompting innovations in client-side interpolation and lag compensation that became the architectural foundation of all subsequent online first-person shooters.
Big Rigs was released in a state so unfinished that it had no collision detection, an opponent truck that never moved, and infinite acceleration in reverse. Crossing the finish line displayed the grammatically mangled "YOU'RE WINNER" — and the game became the definitive example of a product shipped before it was a game at all.
Superman 64 buried its hero in a thick fog and forced players through repetitive "fly through the rings" challenges hampered by broken controls, unreliable collision, and a punishing timer. It became one of the most notorious examples of a licensed game ruined by technical failure.
A precise sequence of steps exploits a flaw in how the game handles interrupted trainer battles, letting players legitimately catch Mew — a Pokémon Nintendo had intended to be unobtainable without special events.
A fully functional Star Fox Arwing left dormant in the code of Ocarina of Time — a debug tool that will fly around and shoot lasers at Link if triggered by a cheat device.
A sexual minigame cut from the game but left intact in its code; a mod re-enabled it, triggering a national controversy that got San Andreas re-rated Adults Only and reshaped ratings enforcement.
Bungie found a bug in Myth II's uninstaller that could erase an entire hard drive — after 200,000 copies had shipped to retailers. The recall cost roughly $800,000, and in the end exactly one person ever fell victim to it.
Where Bungie caught its hard-drive-destroying uninstaller before release, this one shipped. Uninstalling the original 1.0 release deleted system files and left the operating system unable to boot.
A storyline bug made Ultima IX impossible to finish without cheating, saves corrupted, and it ran properly only on 3Dfx cards in the year 3Dfx collapsed. EA had set a ship-or-kill deadline for Thanksgiving 1999.
When Pac-Man faces up, two of the ghosts aim at the wrong tile: an overflow in the targeting code shifts their target to the left as well as ahead. Players had been playing around the bug for decades before anyone documented it.
During a 1997 beta stress test of Ultima Online, a player killed Richard Garriott's supposedly invulnerable avatar with a fire field spell. A server crash had reset the protection, and nobody had switched it back on.
Seven years in development, released unfinished by its publisher over the designer's objections, and reviewed as one of the most bug-ridden games ever shipped. The arguments about it filled Usenet for years.
Bethesda built a world the size of Great Britain with 15,000 towns — and shipped it with so many bugs that it needed patch after patch. Players bought it anyway: 100,000 copies in two days.