From the Super Mario Wiki
King Bomb (キングボム) is a giant Bob-omb that is summoned by a Magikoopa in the Super Nintendo Entertainment System game Super Mario RPG: Legend of the Seven Stars. It uses Big Bang, a powerful magic attack, so it must be destroyed quickly. Mario's Fire and Jump attacks work very well because they are King Bomb's weaknesses and King Bomb has extremely low Magic Defense. A King Bomb is also used by Punchinello in a last-ditch effort to destroy Mario, Mallow, and Geno, but it only ends up crushing him and not even hurting Mario's party.