Throughout your adventure, you’ll unlock challenge levels that put you up against a set of enemies that stand between you, a Green Star, and possibly the next set of levels in a given world. Your time limits in these challenge levels are not very long, so you have to work fast to win and get a good score bonus at the end of the battle.
Here, you face off against two Chargin’ Chucks. You can jump on their heads even while they charge at you, just don’t let them hit you with that charge. The first hit they take knocks off their helmet; the second will finish them off. Beating them earns you the Green Star and a pile of Coins. Their defeat links the first island of World 1 to the second, and reveals 1-3.