One night, five mysterious Sky Crystals fall to Earth. Mario discovers one and eagerly shows it to his friends. Suddenly, a surprise invitation arrives from Bowser: “Hey, chumps! I'm throwing a Big Bowser Bash to apologize for being such a jerk!” Naturally, everyone is suspicious, but the promise of free food is too tempting to resist. They head to Bowser’s Castle, hoping for a party, but it's a trap. Bowser steals the Sky Crystal and uses a new device called the Minimizer to shrink everyone down to tiny size. With four Sky Crystals still missing, Bowser launches the mini-sized heroes to the far edge of the kingdom to keep them out of his way. Their adventure begins, small in size and facing a world full of giant challenges.