Stomps, throws his head back, and roars. Does 7% and has a windbox.
Takes no knockback.
Giga Bowser first appeared in Super Smash Bros. Melee as a hidden boss in Adventure Mode. To get to him, Adventure Mode must be done on Normal difficulty or higher, in 18 minutes or less, and with no continues. Giga Bowser also appeared in the final event in Melee as an opponent, alongside with Ganondorf and Mewtwo. Giga Bowser would eventually return in Super Smash Bros. Brawl and Super Smash Bros. for Nintendo 3DS and Wii U, but this time as a semi-playable character in Bowser's Final Smash. He reprises the same role in SSF2.
Strictly speaking, Giga Bowser did not appear in any Mario games, despite being a Mario character. Giga Bowser is likely based on the tradition of final boss fights in Mario games involving Bowser growing to gigantic size; this first appeared in Super Mario World 2: Yoshi's Island, featuring a massive version of Baby Bowser.