Missingno, a mysterious pokemon that was left in the game that is known to distort and corrupt the player's save file. It has reached a certain level of publicity when red/blue were released to the US, bewildering both the public and the press alike.
The Lore Behind Missingno[]
Rumor has it that missingno was created by a failed science experiment. The scientist had no idea as to what creature they had just created. Apparently,Missingno had released a raid on the pokemon region he was in and distorted everything about it, making it inaccesible to players.
What Really Happened, According to Nintendo[]
During development, the creators of nintendo had intended to put a pokemon known as 'kangaskhan'--an evolution of Cubone. Kangaskhans are said to have a 100% female birth rate, indicating that marowak, the only evolution of cubone that is able to become a male, was to mate with Kangaskhan.. However, upon birth, Kangaskhans are said to perish immediately after, and in order to keep their mothers close, the infant dons the mother's skull, thus classifying it as a 'cubone.' That said, not only would it contradict the lore, but one would assume that it would be too morbid for the target demographic. Nintendo scrapped the idea, but it would be too expensive and time consuming to take the data out entirely. They left the data in the game, and without sprites, a name, or a Pokedex number, it became the famed 'missingno.'
Forms From Generation 1 and 2[]
Missingno has about 5 different forms. Most forms are scattered around the first game while some (maybe 1 or 2) are in another. The first form is a glitchy block of text. The 2nd form seems to be a ghost pokemon. The 3rd from starts as a fossil of an aerodactyl. The 4th form takes place as a undead revived fossil of an kabutops. Missingno.'s final known form basically looks like a white background with random clusters of pokemon center tiles
Missingno in its 5 different Forms
Forms From Generation 3[]
Eventually, MissingNo. Took on another form--Two question marks.
The question mark form