Bowser Jr.'s Robot Reactor

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

Mix Planet
It is found right before Mario visits the Tech Planet and encounters Megaleg. The Mix Planet is a hollow planet with holes in it like swiss cheese. Inside the middle of it is a small black hole that will kill Mario if he falls into it. The planet is simply a mixture of: Dangers, Rewards (Coins and 1-Up Mushrooms), and Cosmic Bullet Bills. A Cosmic Bullet Bill cannon rapidly fires Cosmic Bullet Bills at Mario, which he must lead to the cages (as seen in the screenshot) to break them and collect the prizes inside. This is a pre-boss planet with no warning, so be aware that Megaleg lies ahead.

Tech Planet
This is where Megaleg is found and battled. It is fairly small and orange, with many technology symbols all over it as if it were some kind of mothership styled planet. It also has small rectangular areas on it that are transparent and seem to have something inside them, possibly computer based.

Wood Planet
It is very small and has layers of wood; orange, yellow, and red wood. All it really consists of is a readable sign post. It should also be noted that the Yoshi Planet is also composed of wood.