Things You'll Need
Instructions
Select "Colosseum Battle" from the main menu. Select either "Solo Battle" to play by yourself or "Gang Battle" for a battle with up to four players.
Select the desired battle type. Select "Register Pokemon" and "GBA Pokemon." If you previously registered a team, select "Yes" to overwrite it.
Insert the "Pokémon Ruby" or "Sapphire" game into the Game Boy Advance. Connect one end of a GBA cable to the Game Boy Advance. Connect the other end to a GameCube controller port. Power on the Game Boy Advance.
Select "Register" to transfer your team to the "Pokémon Colosseum" game. When the transfer completes, turn off the Game Boy Advance power.