Red Power Star
From the Super Mario Wiki
The Red Power Star is a unique Power Star in Super Mario Galaxy. It is located only in the Gateway Galaxy after Mario enters the Gate in the Comet Observatory. There, Mario finds Rosalina as well as a Red Luma who allows him to use Red Stars to become Flying Mario so he can collect one hundred Purple Coins for the Red Power Star. After collecting the Red Power Star, Mario has access to Red Stars in the Comet Observatory and can fly around the place at his leisure.