The Star Cures are items that appear in Mario and Luigi: Bowser's Inside Story. There is three in the entire game and together, they make up the Miracle Cure.
The Star Cures are all small, blue and circular objects. Each of them has a star in the middle of them with the colors red, green, and yellow.
During the middle of the story and defeating Bowser in a battle, Mario and Luigi encounter Dr. Toadley who tells them about the Star Cures. He says that they have the power to cure the Blorbs and each of them is being held by a Star Sage. Mario and Luigi decide to head out and search for them (with Bowser over-hearing the entire story and heads out to find them on his own).
Star Cure 1
Dr. Toadley tells Mario and Luigi that the first Star Cure is located in Dimble Woods and the Star Sage is Durmite. However, Mario and Luigi tell Toadley that they already defeated Durmite early on in their quest in Bowser's body. Mario and Luigi then head back into Bowser's body and into the Energy Hold where they endure a wild goose chase and eventually find and defeat Durmite (who's real name is actually Wisdrum). She gives the two the first Star Cure and Mario and Luigi head out for the second one.
Star Cure 2
The second Star Cure is located at Bowser's Castle where Mario and Luigi decide to let Bowser take over. Bowser remembers that he has a Star Cure locked away in his Treasure Chamber in a safe grateful that Fawful hasn't been down there yet. However, before he can retrieve the Star Cure, Bowser is suddenly runned over by the Fawful Express and gets crushed by a large boulder. Mario and Luigi head to the Rump Command to revive Bowser and turn him big. Bowser manages to derail the Fawful Express but he can't remember the combination to his safe. Starlow suggests to Mario and Luigi to head to the Memory Banks in order to solve the problem. Mario and Luigi manage to reconstruct Bowser's memory and Bowser opens the safe. Unfortunately, Bowser gets pushed into the safe by Private Goomp, Sergeant Guy, and Corporal Paraplonk and starts heading for an unknown location. Bowser, knowing he's trapped, decides to swallow the Star Cure thinking he has no more use for it. Mario and Luigi head to the Gut Check and they retrieve the second Star Cure.
Star Cure 3
The third and final Star Cure is being guarded by Chakron who is located very high over Plack Beach. Chakron will only hand over the Star Cure to Mario and Luigi if they can knock him off his "1000 year pose." Mario and Luigi must use the Snack Basket technique in order to knock him over. After they do that, they earn the final Star Cure.
After collecting all of the Star Cures, Mario and Luigi head back to Dr. Toadley's office where he finally creates the Miracle Cure. Using it, the Miracle Cure heads over Toad Town and cures every infected citizen of the Blorbs. The Miracle Cure also breaks down the barriers that was blocking the way the Princess Peach's Castle. Mario and Luigi are finally ready to confront Fawful.