One night, five mysterious Sky Crystals fall to Earth, and Mario excitedly shows the one he finds to his friends. Just then a suspicious invitation arrives from Bowser: "Hey, chumps! I'm throwing a Big Bowser Bash to apologize for being such a jerk!" Everyone is wary, but the promise of free food proves too tempting, and they head to Bowser's Castle hoping for a party — only to walk straight into a trap. Bowser steals the Sky Crystal and uses a new device, the Minimizer, to shrink the heroes down to tiny size, then flings them to the far edge of the kingdom to keep them out of his way. With four Sky Crystals still missing, their adventure begins — small in stature, against a world full of giant-sized challenges.