SMB 2 - Defeating Birdo in World 1

 In the first level of Super Mario Bros. 2, you have to fight a boss referred to as "Birdo." You'll come face to face with her when you climb up multiple vines and clouds. Birdo defends herself by walking back and fourth and launching eggs from her mouth. To defeat Birdo, you have to hop onto her eggs mid-air and throw them back. Throw three eggs at Birdo, then she passes out (or dies). After the battle is over, you'll enter a giant bird's mouth and you'll be taken to the next level.