Beat the Minions!
From the Super Mario Wiki
Beat the Minions! is the final post-game level of the Bowser Jr.'s Journey mode of Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey, and by extension, the final level of the entire game.
Each round has a dark Koopaling as the captain or first officer, who all use the same Captain Commands as their normal versions (apart from Ludwig's Negotiate), whereas the last round has all of them as troops with a dark version of Bowser as the captain. Almost every enemy in this level, including the Koopalings and Bowser, is affected with Malatone Formula:X.
After completing the level, Bowser Jr. and his troops will briefly celebrate while the game congratulates the player for completing the entire quest.