From the Super Mario Wiki
Minis Marching is a post-game level in Bowser's Castle in the Bowser Jr.'s Journey mode of Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey.
The level has four battles. The first battle has three Mechakoopas, four Buzzy Beetles, a Spike Top first officer, and a Mechakoopa captain. The second battle has five Spinies, two Spikes, a Ninji first officer, and a Spiny captain. The third battle has two Spike Tops, four Bob-ombs, one Spike, and a Buzzy Beetle first officer and captain. The fourth and final battle has six Ninjis, one Bob-omb, and a Spike first officer and captain.