A Traitor's Fate
From the Super Mario Wiki
A Traitor's Fate is a post-game level in the Bowser Jr.'s Journey mode of Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey.
Private Goomp, Corporal Paraplonk and Sergeant Guy are walking around Bowser's Castle when the other minions berate them for betraying Bowser and locking him in a safe. The trio feel remorseful for their treason, and Bowser Jr., who was walking around bored, asks the trio to fight with him. After defeating them all, they join Bowser Jr.'s team.