Professor E. Gadd's Research
From the Super Mario Wiki
Professor E. Gadd's Research is the second bonus level of the Beanbean Kingdom in the Minion Quest: The Search for Bowser mode in Mario & Luigi: Superstar Saga + Bowser's Minions. This level is unlocked after completing Larry's Fortress and brewing at least one drink in Starbeans Cafe in the main game.
Captain Goomba, Captain Shy Guy, and the assisting Lakitu begin looking for Boos in a nearby cave, along with a few Tail Boos. When they find and recruit some, they stumble across Professor E. Gadd, who is performing his usual research. As the Goomba Squad leaves, E. Gadd reveals that he is working on a time machine, preceding the events of Mario & Luigi: Partners in Time.