Gen 1 Glitches

Pokémon Red and Blue are held together with tape. The games shipped after a development cycle that nearly bankrupted Game Freak, onto a console Nintendo had already written off, and the code shows it. The bugs became a shared folklore — the rare case where a generation of kids collectively reverse-engineered a product by rumor.

MissingNo.

The famous one. Talk to the old man in Viridian City who demonstrates catching a Weedle, then fly to Cinnabar Island and surf along the strip of coastline on the east edge. You will run into a scrambled column of pixels called MissingNo.

The cause is mundane and elegant. The tutorial temporarily overwrites the buffer holding your name so the demo can display “OLD MAN”, and the game never fully restores it. The Cinnabar coast tiles have no encounter table of their own, so the game reads whatever is sitting in that memory as a list of species indices — which is now the letters of your name. Different names summon different glitch Pokémon. You are literally battling your own save file.

Why it duplicated your Rare Candies

Encountering MissingNo. bumps the quantity of the sixth item in your bag to over a hundred, which is why an entire playground economy ran on it. This is a side effect of the glitch species writing into memory it has no business touching — the same reason it scrambles your Hall of Fame records and corrupts your sprites until you reset. The damage is almost always cosmetic, which is the only reason the trick has a good reputation.

The truck

There is a truck near the S.S. Anne dock in Vermilion City. It is real, it is in the game data, and there is nothing under it. The rumor claimed that using Strength to move it revealed Mew, which is false in every version. What makes the story interesting is that the truck is otherwise unreachable — the ship departs before you can get Surf — so the object exists in a place almost no player should ever stand. An unexplained asset in an unreachable spot is exactly the shape of thing a rumor grows on.

The Mew glitch that does work

Mew was inserted late by Shigeki Morimoto into a few hundred bytes of leftover space, never intended to be obtainable. It is obtainable anyway. The trainer-fly glitch involves getting into a trainer's line of sight and escaping the battle prompt, which leaves the game about to start an encounter using your Special stat as the species index. Get your Special to exactly 21 and you meet a level 7 Mew. No cheat device, no event distribution — just an arithmetic accident.

Bugs that shaped the game

Not everything broken was exploitable. Focus Energy was supposed to quadruple your critical hit rate and instead quartered it. Ghost-type moves were coded to do nothing at all to Psychic types, removing the one intended counter and leaving Psychic catastrophically dominant for the entire generation. And any move, at any accuracy, missed roughly one time in 256 because of an off-by-one in the accuracy check — a small unfairness quietly baked into every battle anyone played.