Cosmic Mario is a character that appears in Super Mario Galaxy. Its physical shape is identical to Mario, while its outer appearance is blue with stars, resembling space. It also has a high-pitched voice. If Mario enters a galaxy when a Cosmic Comet is orbiting a galaxy, Cosmic Mario appears at the beginning at the level and challenges the player to a race. The player must then race through numerous obstacles and reach the Power Star before Cosmic Mario does. If Cosmic Mario manages to reach the Power Star first, Mario will lose a life and must restart the race. Colliding with it during the race causes it to release Star Bits.
At the start of a race, if the player holds the up, then when the timer hits 2, and then hits just as the race starts, Mario or Luigi will get an extra boost at the beginning of the race, shown by a yellow color appearing on Mario/Luigi, shrinking gradually as a marker of the end of this effect. This is similar to the Rocket Start from the Mario Kart games.
A similar entity based on Cosmic Mario appears in Super Mario Galaxy 2 and Super Mario 3D Land in the form of the Cosmic Clones. Other similar entities are the Cosmic Spirit from Super Mario Galaxy 2 and Mummy-Me from Captain Toad: Treasure Tracker.
Cosmic Luigi also appears, replacing Cosmic Mario when playing as Luigi. It is very similar to Cosmic Mario, with the only major difference being that it takes advantage of shortcuts more often and uses a large amount of Long Jumps, making it faster and harder to beat than its counterpart.
In Super Mario Galaxy 2, despite not being in the game while playing as Luigi, Cosmic Clones behave very similarly, being slightly faster.
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