Goomba Squad, Go!
From the Super Mario Wiki
Goomba Squad, Go! is the first compulsory level of the Bowser Jr.'s Journey mode of Mario & Luigi: Bowser's Inside Story.
After being given the recipe of Skeletone Formula:D, the Koopalings (except for Lemmy, who decides to stay and guard the castle) decide to go and find the ingredients. Bowser Jr. wants to do so, too, to impress his father. As a test of strength, Ludwig sends Captain Goomba and the other captains to fight Bowser Jr.
During the first round, Bowser Jr. has only one Mechakoopa as a troop. In the second round, he summons two more.