by Elliot Gavin Keenan
In Pokémon Gold/Silver/Crystal (Generation 2) there was no legitimate way for players outside of Japan to obtain every Pokémon. The mythical Pokémon Celebi, who resides in a shrine in Ilex Forest, was only obtainable as the result of a special event distribution; at the time, these distributions required a physical setup and a link cable. Due to the declining popularity of Pokémon in the English-speaking world at the time, Celebi was never distributed. This meant that English-language players could not complete the Pokédex.
However, this did not deter all English-language players from completing the game. Users of the fan-made English website Glitch City Laboratories found a specific exploit that allowed the player to generate a Celebi without the use of third-party cheating software such as a GameShark or Action Replay (neither of which were widely used yet).
You may wonder how such a specific, targeted exploit of the game was possible. The important thing to understand about it mechanistically is that in the Generation 2 games, Pokémon and moves (and items) were coded in a single table defined by index numbers. That is to say, a single table encoded different types of information (and hence, the number of Pokémon was exactly equivalent to the number of moves — 251). See below for an example of an index number table:
Interestingly, there is one move in the game that no Pokémon could legitimately learn: Struggle, index number 165, shared with Ledyba. For this reason, Ledyba is actually the only Pokémon not obtainable using this exploit. You can see a list of Pokémon by index number in Gen 2 here.
This exploit does not produce glitch Pokémon when performed correctly, although if there is no move in the correct slot it will produce a bad clone of the glitch Pokémon ?????. In theory, there are only 4 glitch Pokémon in Gen 2 because the index numbers are stored in one byte (8 bits) — meaning it can only hold exactly 255 entries, and the first 251 are valid. (Getting rid of these bad clones is very difficult; perhaps a future blog post!) Actually, incorrect performance of the exploit can cause widespread corruption of game data and affect the entire game, potentially making in unplayable.
Point is, though, that any valid Pokémon except for Ledyba can be produced using the Celebi Egg Glitch, despite its title. The move Splash (#150) will result in Mewtwo, for example. But the move Beat Up is what we are interested in, since it has #251 — Celebi.
You must be wondering by now, how do I perform the glitch?! Well, there’s an article for that as the procedure requires a great deal of precision to get the Pokémon you want. Good luck!
Dr. Grimaldi’s Takeaway:
This post is excellent! It demonstrates the power and perseverance of the Pokémon community to problem-solve an issue that appeared to be an unsolvable problem through creative thinking and extensive knowledge of the game’s code.