The Power of the Koopalings
From the Super Mario Wiki
The Power of the Koopalings is the last level in Bowser's Castle (West) in the Bowser Jr.'s Journey mode of Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey.
Despite wearing himself out from his previous battle with Roy, Bowser Jr. charged foward for one final push towards Bowser's Castle, with the Koopalings (with the exception of Morton, who was still brainwashed) by his side. After defeating lots of enemies, Bowser Jr. tried to tell Roy something. Roy assumed it was since Bowser Jr. is the boss's kid, he falls in line. However, Bowser Jr. said that was not it, and it turned out to be an apology for what happened between them back in Dimble Wood.