Clash of Captains
From the Super Mario Wiki
Clash of Captains is the ninth captain command in the Minion Quest: The Search for Bowser mode of Mario & Luigi: Superstar Saga + Bowser's Minions. It costs six CP to use. When used, the captain will challenge the opposing captain to a one-on-one battle, but not before proceeding to take damage from the allies that try to stop him. The move (and the battle) ends when one of the captains is defeated. Captain Goomba and Private Goomp are the only ones that can use it.
This captain command returns in the Bowser Jr.'s Journey mode of Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey under the name Showdown. Bowser Jr. can use it if he is set as a Melee type, it costs five CP to use, and the first officer will defend him on his way to the other captain. There are lots of enemy captains, such as Beef, who use this command as well.