One of the few items on the list that’s 100% legit, MissingNo is by far one of the most famous video game glitches of all time. Performing a particular set of actions in the original Pokemon games would trigger the appearance of MissingNo, an unofficial glitch Pokemon, on the shore of Cinnabar island.
So what was it? The clue is in the name. MissingNo, which stands for ‘Missing Number’, is indexed as Pokemon number 000; while it technically “existed”, it wasn’t an official creature, usually taking the form of a bunch of scrambled pixels.
When players would encounter a random battle, the game would assign values to a wild Pokemon in a data buffer, but due to a mistake the Cinnabar Island shore didn’t actually do this and instead pulled the information from the last location the player visited. To trigger the appearance of MissingNo, the player would first have to go through the old man’s Pokemon-catching tutorial, which assigned the player’s name in the data buffer. Then, if the player immediately travelled to the Cinnabar Island shore, the game would try to pull the hexadecimal values of their name only to detect they did not match that of a Pokemon, and instead spat out a glitch: MissingNo.
After encountering MissingNo, the player’s sixth listed item would usually multiply, hence many people referring to this as the “Infinite Rare Candies cheat”. But MissingNo could also bring about a number of damaging effects, one of which scrambled the final Hall of Fame data. MissingNo could be caught – it acted like a fully functioning Pokemon – but doing so caused a few other mishaps, such as messing up the player’s sprite.