After Super Mario Bros. 2, Mario and his friends convince themselves that Subcon was nothing more than a shared dream and carry on with their ordinary lives. That peace is shattered when Wart stages a comeback, toppling the King of Subcon in their absence. The heroes must once again take up arms against Wart's army — the Birdo trio, Mouser, Tryclyde, Fryguy, and Clawgrip all standing in their way.