Event 9: The Monster Beneath the Earth
From SmashWiki, the Super Smash Bros. wiki
The Monster Beneath the Earth (地の底に巣くう怪物, Monster Nesting under the Earth) is the 9th solo event match out of a total of 41 in Super Smash Bros. Brawl. The player begins on Castle Siege as Ike facing two Diddy Kongs. If the player does not defeat both Diddy Kongs before the stage moves to the third level of the castle, the player must also face a Giant Donkey Kong, who deals more knockback that usually KOs the player in one hit.