Rainbow Star

The Rainbow Star is an item that appears in Super Mario Galaxy and Super Mario Galaxy 2; it is the Super Mario Galaxy equivalent of the Super Star, used to prevent confusion between Super Stars and Power Stars. When collected, it transforms Mario into Rainbow Mario (or Luigi into Rainbow Luigi), causing him to become rainbow-colored and leave a trail of light behind him whenever he runs. In this form, he is invincible, releases Star Bits from damaging enemies, can break through certain objects and obstacles (such as Chomps and Boulders), can run faster, and can jump both farther and higher. As the power-up begins to wear off, the music, along with Mario's running speed, will get faster and faster until it wears off completely. The only mission in Super Mario Galaxy where a Rainbow Star is required is The Golden Chomp.

Missions
Super Mario Galaxy
 * Good Egg Galaxy: King Kaliente's Battle Fleet
 * Honeyhive Galaxy: Bee Mario Takes Flight, Trouble on the Tower, Big Bad Bugaboom
 * Battlerock Galaxy: Breaking into the Battlerock
 * Ghostly Galaxy: Luigi and the Haunted Mansion, A Very Spooky Sprint, Beware of Bouldergeist
 * Gusty Garden Galaxy: The Dirty Tricks of Major Burrows, Gusty Garden's Gravity Scramble, The Golden Chomp
 * Dusty Dune Galaxy: Blasting through the Sand
 * Gold Leaf Galaxy: Star Bunnies on the Hunt, Cataquack to the Skies, When It Rains, It Pours
 * Deep Dark Galaxy: The Underground Ghost Ship, Bubble Blastoff
 * Sand Spiral Galaxy: Choosing a Favorite Snack

Super Mario Galaxy 2
 * Sky Station Galaxy: Peewee Piranha's Temper Tantrum, Storming the Sky Fleet
 * Yoshi Star Galaxy: Spiny Rainbow Romp
 * Spin-Dig Galaxy: Digga-Leg's Planet
 * Shiverburn Galaxy: Octo-Army Icy Rainbow Romp

Super Mario 3D All-Stars

 * North American website bio: "For a short time, Mario pulses with all the colors of the rainbow and runs at superspeed, knocking down any enemies in his path."

Trivia

 * The Rainbow Star is the only power-up in Super Mario Galaxy 2 that does not appear as a souvenir in the engine room of Starship Mario.
 * If the player touches another power-up while invincible in Super Mario Galaxy, it flies high into the air. It comes back after a while, however.
 * The music associated with the Rainbow Star is a remix of the music played when Baby Mario acquires a Super Star from Super Mario World 2: Yoshi's Island.
 * The Rainbow Starchute in Mario Kart Tour is reminiscent to the Rainbow Star, although it has eyes.