From SmashWiki, the Super Smash Bros. wiki
Unlikely Allies (known as Our Saviours in PAL versions of the game) is a co-op event match in Super Smash Bros. for Wii U. In it, player 1 controls Palutena and player 2 controls Ganondorf with two stocks each. They must defeat 16 Mr. Game & Watches, with four of them appearing on stage at a time, with the exception of the last four which appear in pairs. The first 12 Mr. Game & Watch range from slightly small to normal, and are easy to KO. The following two Mr. Game & Watches will be giant and harder to KO. The final two Mr. Game & Watches will be even bigger and metal as well.
This event is unlocked by clearing Poisonous Planet and unlocking Mr. Game & Watch. Completing the event does not unlock any further paths. Once both the event is completed and Wario is unlocked, the right path is revealed.
By clearing the event within 80 seconds on normal or hard difficulty, one can obtain the Desperate Immortal Shield.