Plot

Isle Delfino

The game takes place on the tropical resort of Isle Delfino ( for "dolphin"). The island is mainly inhabited by the races Piantas and Nokis. Isle Delfino is in the shape of a . The island comprises ten available locations. Delfino Plaza is Isle Delfino's capital and the game's main hub.

Mario sets out for Isle Delfino for a vacation with , her long-time steward , and some other , hoping for a relaxing vacation. Upon arrival, Mario finds that the once-pristine island has been polluted and plastered with . As a result of this , sun-shaped objects called "Shine Sprites", the island's sources of power, have disappeared, and the island is covered in a perpetual shadow. The culprit seen spreading the graffiti is disguised as Mario (referred to as "Shadow Mario"). Mario is promptly arrested as he arrives at the island. He is put on trial, found guilty, and ordered to clean up the mess and return the Shine Sprites. To help with the cleaning, Mario finds FLUDD, a powerful water cannon which is toted like a . Mario sets out on an adventure to clear his name and locate the real criminal, while restoring tranquility and order to Isle Delfino.

After numerous incidents, Mario follows Shadow Mario , who has kidnapped Princess Peach, to an . There, Mario defeats a huge robot being controlled by Shadow Mario. It is then revealed that Shadow Mario's real identity is , the son of . Bowser Jr. takes off in a with Princess Peach, whom he believes is his mother, thanks to Bowser. He is last seen heading for Corona Mountain where his father is awaiting. After Mario beats Shadow Mario in all of the locations, he enters Corona Mountain, defeats Bowser and rescues Princess Peach, however, FLUDD becomes damaged and is supposedly beyond repair.The Toads repair FLUDD shortly afterward and Mario, Peach and the others then begin the vacation.