Everything Pokémon: Pokémon Facts Book 1

Pokemon Fact #126

For those who don't know, MissingNO. is a glitch that appeared in Pokémon Red and Blue that would often cause the game to freeze or become completely unplayable. It was possible to catch MissingNO. by travelling along the eastern shore of Cinnabar Island, though besides duplicating items indefinitely, there wasn't much point to trying to catch one. Although the MissingNO. glitch has been well documented, most people don't know it can be manipulated to achieve even more interesting results. For example, if you name your character DxDyDz, it's possible to encounter a MewTwo while performing the MissingNO. glitch. Going one step further, if you already have a Mew in your party, then it's even possible to encounter a level 142 MewTwo in the same area, though the chances are incredibly low.