Super Mario 3D World: 4-B -- Fire Bros. Hideout #1

The Fire Bros have created a few hideouts hidden throughout the Sprixie Kingdom. The first one can be found through a pipe south of the castle. There are three Fire Bros in the room and you have 100 seconds to kill them. They'll jump around, so let two of them stand across from each other and stand between them briefly. They'll throw a fireball at each other, defeating each other so you don't have to. Stomp the third one to make a Green Star appear. You'll also get access to a Sprixie House with a stamp of the blue Sprixie Princess.