The Power of Junior
From the Super Mario Wiki
The Power of Junior is the last level in Bowser's Castle (East) in the Bowser Jr.'s Journey mode of Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey.
After Bowser Jr. has taken on all the captains at least once, Captain Goomba rallies the other captains for Bowser Jr. to take on all four of them at once as one final test, with the addition of King Bob-omb as a "game-changer". If King Bob-omb is not defeated in under 90 seconds, he will explode and instantly defeat any surviving allies. After the battle, Captain Goomba tells Bowser Jr. that his minion spirit was on fire and that he will head with the other former captains that they should guard the fort with Lemmy. Bowser Jr. tells Captain Goomba that he was his "punching bag" and that he exists just to entertain him. He then realizes that he never had gotten to his 20th victory yet and that he will need at least 15 more wins when they get back to the castle. Captain Goomba was still worried about his math problems since he still does not know how to subtract yet. The Koopalings tell Bowser Jr. that they were ready to head on to Dimble Wood to find the Giga-carrot. Ludwig once again tries to teach him more information on how to battle, but Bowser Jr. disagrees to learn more. Bowser Jr. and the Koopalings then set off to find the Giga-carrot. The Best Fitness Friends, watching the Koopalings leave the castle, prepare to sneak into the castle so Fawful can take over, in which they wanted to later overthrow him.