Bowser Jr.'s Lava Reactor

Bowser Jr.'s Lava Reactor is a Bowser Jr. galaxy in Super Mario Galaxy. This is where Mario battles King Kaliente for the second time and receives a Grand Star. The galaxy is an extremely large sun made out of lava with very few rocks.

This planet is small, made of dirt and is half-gone due to its Black Hole core eating away at its surface. There are several Goombas and one Bullet Bill launcher. There are also several cages that can be broken by a Bullet Bill that contain items such as coins, a 1-Up Mushroom and a Launch star.

This sun is large and is made up solely of lava. There are several sinking platforms around its northernmost region in a circle formation, with more sinking platforms in a path-like formation across its southernmost region. This planet is home to King Kaliente and is where Mario fights him for the second time.

Enemies

 * Bullet Bills
 * Octopuses
 * Goombas
 * Lava Bouncers
 * King Kaliente (Boss)

King Kaliente's Spicy Return
Upon entering the galaxy, Mario will land on a small planet with a few Goombas, a Bullet Bill Blaster, a caged 1-Up Mushroom, and a caged Launch Star. Mario will have to lure a Bullet Bill to the cage to smash it open, gaining access to the Launch Star. The Launch Star will shoot Mario to the Lava Reactor's surface, which is entirely lava, except for a few sinking platforms. There, Mario will encounter two brown Octopuses that he will have to defeat to access another Launch Star. From there, Mario will encounter Bowser Jr., who will make him fight a much stronger, dark version of King Kaliente while on the sinking platforms. Upon defeating King Kaliente for the second time, Mario will receive the sixth Grand Star.

Trivia

 * This level is the only optional boss battle, as one can get the 60 Power Stars required without this Grand Star.
 * It's unknown how King Kaliente was revived even though the player killed him in the Good Egg Galaxy.