Super Mario 3D World: 5-B -- Fire Bros. Hideout #2
On the west side of World 5 is a small patch of dirt. Approach it and press (A) to reveal a pipe to 5-B. You have 100 seconds to defeat a single Fire Bro. Unfortunately, he's on top of a very tall stack of Goombas. You can either destroy the stack of Goombas or stand on the rising pillars, then jump and stomp. Defeating the Fire Bro will get you a Green Star.