Mario, Luigi and friends decide to head to Daisy's kingdom of Sarasaland for a much-needed holiday following the events of the last film, but Mario and Luigi's grouchy and greedy cousin (taking on the doppelganger identity of "Wario") and his best friend ("Waluigi") have entered the Mushroom World, and teamed up with Sarasaland's deadliest enemies, the reptilian overlord King Wart, and the intelligent alien general Tatanga. Can our friends save Sarasaland before it's merged with Mario and Luigi's world?
