South of World 4-5 on the World Map is a pipe that leads to and underground section. There, you can take on a team of Fire Bros. on their home turf. It’s three-on-one (or more if you’re playing with friends), and the Fire Bros. will aggressively try to keep you away using their fireballs. You also have a mere 100 game seconds on the clock. Once you knock these guys out, you earn a Green Star.