Giga Bowser

Giga Bowser (ギガクッパ, Giga Koopa), is the gargantuan and powered-up version of Bowser. He first appeared as a hidden final boss in Super Smash Bros. Melee 's Adventure Mode and as one of the final opponents the player must face in Event Mode. He eventually made his semi-playable debut in Super Smash Bros. Brawl as Bowser's Final Smash. Having debuted in the Super Smash Bros. series, Giga Bowser is considered a part of the Super Smash Bros. universe, even though the character he is based on, Bowser, is from the Mario universe.

Adventure Mode
In Melee, Giga Bowser appears as a hidden final boss. To encounter him, all previous stages in the mode have to be completed in under 18 minutes and on Normal difficulty or higher and without using a Continue. If done correctly, a new cutscene will be shown after Giant Bowser is defeated - his KO'd trophy will return to the stage and be struck by lightning, causing it to come back to life as Giga Bowser. Defeating Giga Bowser leads to the completion of the Adventure Mode; defeating him without using a Continue also rewards the player with his trophy.

Event 51: The Showdown
Giga Bowser also appears in Melee's final Event Match, alongside Ganondorf and Mewtwo. The match is similar to his appearance in the Adventure Mode, but with the presence of two teammates. Clearing the Event Match allows the player to use Final Destination as a Versus stage, as well as rewarding Final Destination's trophy; as an added bonus, clearing the match without losing a stock rewards the player with an exclusive Notice.

Unlike most other bosses, Giga Bowser has a damage percentage as opposed to HP (in both of his appearances) and takes knockback; the player must KO him by knocking him offstage as opposed to merely attacking him.