Viewing a map distortion glitch item in a grassy area
Map distortion glitch items are glitch items found in Pokémon Red and Blue.
These glitch items are capable of causing a map distortion effect after they are viewed in the player's inventory, provided that the player is both in a grassy area and has a player name that is at least four characters long.
These include many of the glitch items with IDs between 0x74 and 0xC3, especially item 0x87, known as ####PkMnぉゥ# #ゥ #ゥC ##.
The cause of the corruption is likely due to a name length overflow caused by the game attempting to print grass tiles in the item's name as control characters, which both have the index number 0x52.
Map corruption caused by the glitch item effect
- TheZZAZZGlitch: Documentation, screenshots in this article (from video)