Find the Invincibility Mushroom!
From the Super Mario Wiki
Captain Goomba, Captain Shy Guy, and Captain Boo find the same Toad they "rescued" from Morton earlier. Although still uninterested in helping the Toad, he bribes them into finding the Invincibility Mushroom for the Little Fungitown arcade. The Goomba Squad battles Gritty Goombas, Limbo Bros, and Hammer Bros. They find two mushrooms, and mistake a Poison Mushroom for the one they are looking for. This explains why Mario contracts Bean Fever later on, as he would end up consuming the Poison Mushroom the squad acquired rather than the true Invincibility Mushroom they found.