Revernd Awesome said:
Hurray for MISSINGNO!
There's actually about 104 of those, ya know. I learned the exact logic behind it a while back. Turns out that the way the old Game Boy games memory works means that there were 255 slots for Pokémon in the original Red and Blue games. Because there weren't that many, the rest were filled with "Missing Number", or MISSINGNO for short. The likeliness of encountering them is set to 0 for the player though, in order to avoid complications. However, in that one area in Cinnibar Island, there is no set limits on what you encounter, other than what you, as a player encounter.
However, when you fly to Cinnibar Island after watching the Old Man catch a Pokémon, the game still has the player set as Old Man. Now, Old Man doesn't have any limits on what he can encounter. Hence, MISSINGNO appears! Of course, there's no actual solid data for MISSINGO, so instead of crashing, the game panics, and draws data from anywhere in order to form an image. Because the game holds all its image data in one folder, the resulting image became, usually, a mess of pixels. Pokémon Stadium, however, decided to show it as one of those Substitute dolls.