when the super mario bros enters a strange new pipe it sends them to a new world where animals trive and live. the super mario bros soon discover a group of talented singers are given a chance to perform in big city where they can show everybody they are the best. they decide to help them acheieve their dreams and show the world how talented they are, in hopes that the moon crew will help Mario and Luigi return home. (this is based off sing 2)

Luigi never regained his memory after being sent to the Underwhere, but still joined the Hero's side. This is the fallout.