Giant Bowser is a minor boss that appears in SSBM and SSBB.

In Super Smash Bros. Melee

In Melee, Giant Bowser appears at the end of Adventure Mode, where you fight him at Final Destination. He may or may not be the last boss. If he is regular colored, he is the last boss. If he is black colored, the last boss may be Giga Bowser (if the time limit is not exceeded and the player does not continue).

Extra appearances include an immensely large version (over twice as large as the normal Super Mushroom Bowser) that appears in Event 25: Gargantuans against the computer controlled, similarly-sized, DK, plus a super tiny Mario and Peach.

In Brawl

Giant Bowser returns with Giant DK in Brawl, and they are joined by a new giant enemy; Giant Charizard. In Event 27: Three-Beast Carnage, Giant Bowser allies with Giant DK and Giant Charizard in attacking New Pork City.

 
Giant Charizard, Giant Bowser, and Giant DK ravage New Pork City.