Bowser Jr's Robot Reactor

Bowser Jr's Robot Reactor is a galaxy featured in Super Mario Galaxy. It is a pretty short galaxy, due to it only having one level. In the level, you will arrive at the galaxy's hub, and after using a Bullet Bill to break open a cage containing a Launch Star, you will be able to launch yourself to a moon where you must fight Megaleg. After defeating Megaleg, a Grand Star is collected and not only is the galaxy complete, but also the entire Terrain is complete as well.

Levels

 * Megaleg's Moon