5) Giga Bowser
First Appearance: Super Smash Bros. Melee (GameCube, 2001)
It was quite the shock when, after defeating Bowser in Super Smash Bros. Melee’s Adventure Mode, Giga Bowser appeared as a secret boss. Massive and hulking, Giga Bowser was a fiercely primal version of the Koopa King, harkening back to the earlier days of the character when he was portrayed as being more ominous and frightening than he currently is. When the devastatingly powerful fighter finally became playable (without hacking!) in Super Smash Bros. Brawl as Bowser’s Final Smash, it forever cemented this take on the character as a mainstay of the series.