From SmashWiki, the Super Smash Bros. wiki
Poisonous Planet (known as Poison Planet in PAL versions of the game) is a co-op event match in Super Smash Bros. for Wii U. In it, player 1 controls Olimar and player 2 controls Samus both under the flowering effect. They must defeat 2 Charizard in a 200 HP match before the players' health are depleted.
This event is unlocked by clearing An Offering of Coins. Completing the event does not unlock any further paths. After both the event is cleared and Mr. Game & Watch is unlocked, the up path is revealed.
Completing the event on normal or hard difficulty awards a Vampire Space Suit equipment.