Mario, Luigi, Peach, and Toad fought Fryguy in World 4-3, and destroyed him, splitting him into four smaller Fryguys, which they defeated as well.
Fryguy flies around in an infinity symbol pattern, shooting fireballs. The player cane easily avoid these, as walking off the left screen makes him/her appear from the right screen. To defeat him, three Mushroom Blocks must be thrown at him. Afterward, he will split into four smaller fireballs. Each takes one hit, and whenever one is destroyed, the remaining ones will move faster. The battle ends once all four are destroyed.