Bowser Jr.'s Robot Reactor

Bowser Jr.'s Robot Reactor is Bowser Jr.'s first galaxy in the game Super Mario Galaxy. In it, Mario fights Megaleg to earn a Grand Star.

Enemies

 * Astro Goombas
 * Bullet Bills

New Mix Planet
This is a very small planet. Mario simply has to get a Bullet Bill to break open a piece of machinery to reveal a Launch Star, and then use that Launch Star to reach the Tech Planet.

Tech Planet
This is where Megaleg is found and battled. It is fairly small and orange, with many technology symbols all over it. It has small rectangular areas on it that are transparent and seem to have computer components inside them.

Megaleg's Moon
Mario begins this level on the New Mix Planet, which contains a Launch Star in a cage. The player will have to lure a Bullet Bill over to the cage to free the Launch Star and reach Tech Planet. Bowser Jr. will appear and summon Megaleg. After defeating Megaleg, Mario earns a Grand Star.

Trivia

 * In the beta version of Super Mario Galaxy, the mix planet is grassy and lacks Star Bit rocks.