In Melee, he appears as a boss. To fight him, Adventure Mode must be cleared on Normal or higher in 18 minutes or less. He will appear after Bowser is defeated. Defeating him without using a continue rewards you with the Giga Bowser trophy. He also appears in Event 51: The Showdown with Mewtwo and Ganondorf by his side. It is possible to use Giga Bowser by using an Action Replay for the Gamecube.
In Brawl, Bowser turns into him by using his Final Smash, Giga Bowser. Here, he is noticeably much larger, scarier-looking and more devastatingly powerful. He appears on the stage for about 12 seconds.