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.

New Mix Planet
This is a very small planet. Mario is required to entice a Bullet Bill to follow him and break open a cage to reveal a Launch Star, and then use that Launch Star to reach the Tech Planet. This metal planet has a black hole that Mario needs to avoid. There are also other cages that can be broken to reveal coins or a 1-Up Mushroom.

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. Megaleg will at first try to step on Mario all the while firing Bullet Bills at him to blow him up. Mario must climb up Megaleg's leg to face two challenges. One, a platform with three Bill Blasters and two, rotating gears that try to send Mario back to the ground. At the top of Megaleg's head, there is a cage and multiple Bill Blasters, use the Bill Blasters to break the cage. Another cage will then pop up and Mario will have to use the Bullet Bills to break that cage and then break the other cage beneath it. If Mario is not fast enough, the cage will regenerate back its smashed pieces. After defeating Megaleg, Mario earns a Grand Star.

Enemies

 * Goombas
 * Bullet Bills
 * Megaleg (Boss)

Planets Visited

 * New Mix Planet
 * Tech Planet

Trivia

 * In the beta version of Super Mario Galaxy, the mix planet is grassy and lacks Star Bit rocks.
 * If you go to the top of Megaleg and use the first person view to look at the mix planet, you will see that it looks like it's beta appearance, instead of being metallic.
 * In a trailer for Super Mario Galaxy 2 a Megaleg like Robot appears on a similar planet.