Giga Bowser is a fictional character in Nintendo's Super Smash Bros. franchise. He is the final boss of Adventure mode in Super Smash Bros. Melee. He is a gargantuan version of Bowser and could only be fought after completing Adventure mode in normal or higher difficulty within 18 minutes and without using any continues. Additionally, he was a villain in the final Event Match, with Mewtwo and Ganondorf (of the Pokémon and The Legend of Zelda series, respectively) fighting alongside him. Giga Bowser is only playable using an Action Replay.
In addition to being much larger than the original king of the Koopas, Giga Bowser looks far more evil, with a slightly smaller head, spikier, scaled shell, surprisingly more muscular physique, and a new curve to his lengthened horns. Giga Bowser is truly an intimidating sight to behold, and rightfully so; he is far more difficult to battle than his smaller counterpart.
Giga Bowser possessed the same moveset as Bowser, but several moves had an elemental effect; for example, his A+Down move could freeze opponents, and his forward Smash was explosive.
Giga Bowser is officially considered to be a Super Smash Bros. character, not a Mario character. In the game, his icon is not a mushroom (as is the case with Mario characters), but a SSB symbol (as is the case with SSB characters). However, in Super Smash Bros. Brawl the final smash of Bowser has a mushroom icon, but this is because it is a move of Bowser's.
Giga Bowser returns in Super Smash Bros. Brawl as Bowser's Final Smash. Many of Bowser's moves are hugely powered up in this form and yet some of them are actually weaker than that of the regular Bowser. He still takes damage from hits but won't flinch, making him possible to KO only by hitting him when off-screen and at the top border of the screen. Because of his large size, he is able to easily attack and KO an opponent. The duration of this move is very short; however there is a glitch that allows the player to remain as Giga Bowser until they self-destruct (cause themselves to be KO'd).