Star Cure

The three Star Vaccines are the ultimate goal for much of the second half of Mario & Luigi RPG 3. Mario and Luigi first learn about the Star Vaccines from Doctor Kokino, shortly after a fight with Bowser.

Kokino tells the Bros. that the first vaccine is held by Imounu, who is at Ekubon's Forest. However, the Marios have already found and beaten Imounu. Later, they discover that Imounu is still inside Bowser's Body, and begin to pursue her. After a battle, Imounu relinquishes the first Star Vaccine on friendly terms.

The second star vaccine, as it turns out, had come into Bowser's possession before the events of the game. He travels to a vault below his own castle to retrieve it. He is forced to do battle with the Gera Express for the star vaccine. Mario and Luigi then need to reconstruct Bowser's damaged memory of the combination to the Star Vaccine's vault. When Bowser opens the vault, however, three traitorous minions, Kurikkī, Heifā, and Patabon, shove him inside. Yellow Star suggests that he swallow the Star Vaccine. He does so, and the Marios escape with it through a warp pipe.

The final star vaccine is held by Chakran, of Musshība Beach. He gives it to the Marios after they successfully knock him out of his "1000 year pose" using Sweet Basket.

When all three Star Vaccines are brought back to Doctor Kokino, he combines them into the Miracle Vaccine, which cures every Toad that has contracted the Metakoro Disease. It also breaks the barriers outside Peach's Castle, allowing the Marios to enter both the castle and the final stretch of the game.