Bowser wonders in the jungle on an Island after being defeated by Mario & Luigi. He heard a strange animal sound. Out of the trees is none other than Donkey Kong. Bowser offers him a deal.
Mario,Luigi,Peach,& Toad are exploring the Dinosaur Island,searching for the species of Yoshis. Their search was interrupted by Bowser,who kidnaps Peach & Toad. Mario & Luigi gets beaten by Donkey Kong,but they were saved by the Green Yoshi,who warns them that Bowser is going after the Great Power.
Bowser contacts the Koopalings to after Mario & Luigi before they get to the Great Power. Mario,Luigi,& Yoshi goes on a journey to Sarasaland. They managed to take the shortcut through the Ghost House where the Boo live. Mario & Luigi transform into their Hammer forms & escapes.
They arrived at Sarasaland where they met Princess Daisy,who reveals that Kongs gave her the Great Power which is called the Super Star to keep it out of wrong hands. The Koopalings attack the Castle. The Mario Bros fought them off,but Luigi gets injured after saving Daisy. Mario faces off with Donkey Kong while Bowser grabs the Super Star and uses it to create Mecha Bowser.
Realized that he has been fooled,Donkey Kong joins Mario & Yoshi to save Peach & Toad. Mario manage to retrieve the Star. Luigi,despite his injuries,join Mario to touch the Star & become invincible. They destroy Mecha Bowser & Bowser falls through the smoke. Peach & Daisy congratulates Mario & Luigi. They also congratulates Yoshi & Donkey Kong for their aid.
Mid-Credits:
Mario,Peach,Yoshi,& Donkey receives an invitation to a competition.