The Amnesiac Koopa King
From the Super Mario Wiki
The Amnesiac Koopa King is the bonus level of Hoohoo Mountain of the Minion Quest: The Search for Bowser mode in Mario & Luigi: Superstar Saga + Bowser's Minions. This level is available after defeating Popple and Rookie in Chateau de Chucklehuck in the main game.
The assisting Lakitu informs the Goomba Squad that Bowser had been spotted in Hoohoo Village. Finding him almost instantly, the captains give chase. They battle Tanoombas, Scaratroopeas, Hammer Bros, and Troopeas, but fail to find Bowser. A Hoohooligan explains that while Bowser managed to break free of Fawful's grasp, he was hit by some sort of rock, then ended up following a food thief.