A Lurking Menace
From SmashWiki, the Super Smash Bros. wiki
A Lurking Menace is a co-op event match in Super Smash Bros. for Wii U. In it, player 1 controls Mario and player 2 controls Luigi, and must defeat Bowser Jr. If the players wait too long, they're forced to fight a Giant Bowser. The players have 2 stocks while the opponents have 1.
This event is available from the start. Completing the event unlocks the down path.
Completing the event within 15 seconds awards a Pity Final Smasher Shoes equipment.