The Original Heavyweights
From SmashWiki, the Super Smash Bros. wiki
The Original Heavyweights is the first single-player event match in Super Smash Bros. for Wii U. In it, Mario must defeat the two heaviest characters in the game, Bowser and Donkey Kong. Clearing this event unlocks Kongo Jungle 64.
This event is available from the start. Completing the event unlocks the Kongo Jungle 64 stage on the challenge board, as well as the right, down, and left paths. Once both the event is completed and Falco is unlocked, the up path is unlocked.
Completing the event without taking any damage awards a Fire Flower Overalls equipment.