Grand Star

The Grand Stars are very large and powerful Power Stars in Super Mario Galaxy and Super Mario Galaxy 2. There are seven in the first game and six in the second game for a grand total of thirteen.

''Super Mario Galaxy
Super Mario Galaxy is the game the Grand Stars first appeared in. As Mario gets these Grand Stars back, he gains access to different parts of Rosalina's observatory. When one is found, a path to the next dome is created. The Grand Stars are the power source of the Comet Observatory's beacon. The beacon is the main source of power of the observatory, but the Grand Stars are needed to power it. Bowser has taken all of the Grand Stars and is using them for his own evil intentions.

''Mario Kart Wii
In Mario Kart Wii, a Grand Star appears as Rosalina's emblem.

''Super Mario Galaxy 2
The Grand Stars re-appear in Super Mario Galaxy 2, once again under the possession of Bowser and Bowser Jr. This time, Grand Stars give power to Starship Mario and open up the portal to the next world.

In this game, the Grand Stars are apparently the power source for Bowser Jr.'s machines and Bowser's huge size. After defeating a machine, it will explode and release a Grand Star. After defeating Bowser, he'll cough up a Grand Star. In the final battle, he is able to swallow it again, leading to one final segment of the battle.

The Grand Stars seem to have a side effect when misused, which caused Bowser to turn tiny after the final battle.

Trivia

 * A Star obtained after defeating Bowser at the end of Super Mario 64 is similar to a Grand Star as it is much bigger than the other Stars. However, it does not have orbs on the end of its points and may simply be a giant Star.
 * In Super Mario Galaxy, it is possible to only have 5 out of the 7 Grand Stars collected to reach the final battle, since Bowser's Galaxy Reactor, where the final battle is, is unlocked after completing the fourth dome.
 * The orbs on the ends of the Grand Star's "arms" make them slightly resemble Shine Sprites.
 * Bowser Jr.'s Fearsome Fleet is the only galaxy where Yoshi is able to pose with Mario when the Grand Star is collected.
 * While there are seven Grand Stars in Super Mario Galaxy, there are only six in Super Mario Galaxy 2.