Giant Kirby is fought on Stage 5 of Adventure upon the Green Greens stage as an optional boss. If the player manages to defeat all of the Kirbys (including the first one who fights alone and the Kirby Team) in 31 seconds or less, a cinematic will play where Giant Kirby drops onto the second floating platform and lands crouching before standing up and smiling.
In Classic Mode, since Kirby is not one of the giant characters on Stage 5, Giant Kirby does not appear as a giant opponent.
Giant Kirby is slightly larger than a regular Kirby with a Super Mushroom and is heavier and stronger than Kirby. If the player defeats Giant Kirby, they will receive the bonus Giant Kirby KO, which awards 10,000 extra points.
Kirby is one of the characters who may be encountered in a Giant Battle in Classic Mode:
Giant Kirby (in an alternate costume resembling an unmasked Meta Knight) is fought on Kalos Pokemon League in Round 2 of Joker's Classic Mode route with Mr. Game & Watch serving as the latter's ally against the former. Giant Kirby is also the only opponent in Joker's route to be fought on a stage other than the latter's home stage Mementos.