Finn and the Mushroom Squad invade Nightmare's warfleet to prevent him from his latest evil plan of merging Robotoplis on a Lost Island to create an evil Nation of Nightmare Enterpirses so that Nightmare can rule Mobius with full force. Finn, Sonic, Mario, Luigi, Yoshi, Goombario, Paraklary and new rookie Natsu fight off the SWATbots and NE troopers on the ships. Nightmare sees what's going on his TV and orders his henchmen Dr. Eggman, Bowser, Bowser Jr., Orbot, Cubot, Mecha Sonic, Kamek, Captain Baslisx, The Beagle Boys and the Koopalings to fight off the Mushroom Squad.