From Bulbapedia, the community-driven Pokémon encyclopedia.
The Pokémon Colosseum Bonus Disc was only available by reserving a copy of Pokémon Colosseum. This disc contained previews of the game Pokémon Colosseum and the movie Jirachi: Wish Maker. It is also one of the few ways to get a Jirachi without hacking the games in North America. In order to get Jirachi, a Nintendo GameCube–Game Boy Advance cable, either Pokémon Ruby or Pokémon Sapphire, and an empty spot in the party is required. With everything connected properly, Jirachi will appear and be transferred to Ruby or Sapphire. The process of obtaining Jirachi can be repeated as long as the game that is receiving Jirachi has not already used this disc. This means that the same person can get multiple Jirachi by using the disc for several different games. If the game that is being used to get Jirachi has the Berry glitch, it will be fixed upon using this disc.
In the Japanese version, the disc contains a Celebi instead and can only be acquired once all of the 48 Shadow Pokémon have been purified. After it has been transferred to the Colosseum save first, it can be transferred up to 48 times directly to all Japanese Game Boy Advance Pokémon games as long as the player has beaten the Elite Four and saved in a Pokémon Center. A Pikachu is also available from this disk.
Pokémon distributed by disc