From Bulbapedia, the community-driven Pokémon encyclopedia.
The Colosseum Master Ball glitch is a glitch in Pokémon Colosseum that enables the player to re-use the Master Ball, or any other type of Poké Ball, as many times as they want. Essentially what this means is that the player needs only to buy one of each kind of Poké Ball during the game.
The glitch is performed by selecting a Poké Ball with the player's first Pokémon's turn and, with the second Pokémon's turn, switching the type of Poké Ball chosen with another Poké Ball in the bag (using the Y button). After the Ball is thrown, the Poké Ball pocket will still have the same amount of Poké Balls, as if the Ball just thrown had not been used.
Sometimes, if using the Master Ball, the game will freeze and bring the "An error occurred" message the GameCube gives when it fails to properly read a game.
Also, if the second Pokémon is using a 2-turn move like Fly or Dig (Or any multiple-turn like Petal Dance) and is on their second or later part of the attack prevents the glitch from working, which causes the thrown Snag Ball to be used.
This glitch does not work on Pokémon XD: Gale of Darkness.