When performed, Bowser roars and transforms into Giga Bowser, a larger and more powerful version of himself. Giga Bowser is able to move freely and has almost a full moveset consisting of modified versions of Bowser's normal attacks, which are generally much more powerful. While in this form, he can take damage but will not flinch or receiveknockback, making him very difficult to KO without self-destructing, though the accumulated damage may allow Bowser to be KO'd more easily after the Final Smash ends. After approximately 20 seconds, Giga Bowser will revert back to Bowser's normal form, ending the move.
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. Then, after defeating Giant Bowser in the final stage, he would transform into Giga Bowser and the player would have to defeat him. Giga Bowser also appeared in the final event in Melee as an opponent, alongside 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 a gigantic size; this first appeared in Super Mario World 2: Yoshi's Island, featuring a massive version of Baby Bowser.
Giga Bowser is the only Transformation Final Smash with missing attacks; he cannot grab, pummel, or throw opponents.
In addition, Giga Bowser has no floor attack, since he cannot receive knockback, nor a ledge attack, because he is unable to grab ledges.