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If you're a Pokemon fan you're already well aware of this infamous glitch! Missingno. was placeholder data left over by the devs whenever they were working on implementing a new Pokemon. There was a rumor going around that the Gen 1 games were supposed to have 190 Pokemon, and the number of leftover slots do correspond with this theory. Missingno. occupies the following slots in Pokemon data:
Only three of those slots have valid sprite data, because the game takes the data from the Kabutops Fossil, Aerodactyl Fossil, and Ghost Sprite. Every other slot grabs sprite data from trainer rosters which is why it results in a glitched pixel. It also is a very large sprite, which is why it takes the game a second to compress the sprite in VRAM when you encounter it. Since the sprite is so large it also overwrites part of the Hall of Fame data in SRAM to actually display a sprite which causes the Hall of Fame Data to get corrupted even if you don't catch it but simply encounter it.
Missingno. causes your sixth item to increase to 128. You can even stack the items to end up with 255 of that item, and can cause other glitches like item underflow in which you can perform Arbitrary Code Execution. (That will get it's own thread.) The item is duplicated since it acts as the "seen" flag for Missingno. It's funny, Nintendo actually addressed this glitch back in the day and told trainers to delete their save and start a new one if they encountered it. Aside from corrupting the Hall of Fame data, Missingno. is harmless.
Code:
1F, 20, 32, 34, 38, 3D, 3E, 3F, 43, 44, 45, 4F, 50, 51, 56, 57, 5E, 5F, 73, 79, 7A, 7F, 86, 87, 89, 8C, 92, 9C, 9F, A0, A1, A2, AC, AE, AF, B5, B6, B7, B8
Only three of those slots have valid sprite data, because the game takes the data from the Kabutops Fossil, Aerodactyl Fossil, and Ghost Sprite. Every other slot grabs sprite data from trainer rosters which is why it results in a glitched pixel. It also is a very large sprite, which is why it takes the game a second to compress the sprite in VRAM when you encounter it. Since the sprite is so large it also overwrites part of the Hall of Fame data in SRAM to actually display a sprite which causes the Hall of Fame Data to get corrupted even if you don't catch it but simply encounter it.
Missingno. causes your sixth item to increase to 128. You can even stack the items to end up with 255 of that item, and can cause other glitches like item underflow in which you can perform Arbitrary Code Execution. (That will get it's own thread.) The item is duplicated since it acts as the "seen" flag for Missingno. It's funny, Nintendo actually addressed this glitch back in the day and told trainers to delete their save and start a new one if they encountered it. Aside from corrupting the Hall of Fame data, Missingno. is harmless.