Following the events of Super Mario Bros. 2, Mario and his friends come to believe that their adventures in Subcon were all just a dream. They move on with their lives — but the peace does not last. The villainous Wart resurfaces, and in their absence he has seized power by overthrowing the King of Subcon. Now Mario and his companions must confront Wart's forces again, including the Birdo trio, Mouser, Tryclyde, Fryguy, and Clawgrip.