Mario and Luigi embark on the adventure of their dreams in a hilarious action RPG that combines the resort world of Pi’illo Island with the wild landscapes of Luigi’s imagination, where anything can happen. Meet a host of hilarious characters as you strive to rescue Princess Peach and help Prince Dreambert free his petrified Pi’illo people from the bat-king Antasma’s curse.

One day in the Mushroom Kingdom, Princess Peach, Mario, Luigi, Toadsworth, and some Toads are invited to Pi'illo Island, which is said to contain a special power that makes people fall asleep. During the flight, a dark pillow falls onto a blimp and transforms into a dark figure who Mario defeats. After defeating him, the blimp malfunctions and crashes into the Pi'illo Blimport. However, it is revealed that it was all Luigi's dream. The group proceeds to Pi'illo Castle, where they meet Starlow. Mario and Luigi go to a room where Peach and Toadsworth accidentally set off a test platform sending them to ancient Pi'illo ruins. Mario & Luigi follow and eventually find Peach and Toadsworth, as well as a Pi'illo, which later turns out to be Prince Dreambert. They find a collection room where Luigi takes a nap on the pillow. After everyone gathers in the collection room, a Dream Portal opens a portal to the Dream World. The dark figure from Luigi's dream pulls Princess Peach into the Dream World. After Mario chases after Peach into Dreamy Pi'illo Castle, with the help of a dreamy version of Broque Monsieur, he comes across Dreamy Luigi, Luigi's dream representation, who assists Mario through his treks in the Dream World.