Bowser's Galaxy Reactor

Bowser's Galaxy Reactor is the final level in Super Mario Galaxy. It is located in the center of the universe. This is where the final Grand Star is located. It features the final battle between Mario and Bowser. Bowser Jr. watches from the sidelines on his airship with the damsel in distress. After this battle, the galaxy collapses, transforms into an huge black hole, and begins sucking up the entire Universe. The Lumas throw themselves into the hole and reverse its effect; the Universe is reborn, and Mario, Peach, Bowser, and everybody else land safely back in the Mushroom Kingdom.

Traversing the Galaxy
The galaxy contains seven planets (not including the three planets in which Mario battles Bowser). The first is a planet with spotlights that change the direction of gravity. This planet is reminiscent of the castle. The second is a spherical planet with a lava core and a few rocks. This planet is reminiscent of the flame half of the FreezeFlame Galaxy. The third is the same with an ice core and ice blocks. This planet is reminiscent of the freeze half of the Freezeflame Galaxy. The fourth planet has a sand core with rocks and firebars. This galaxy is reminiscent of the Dusty Dune Galaxy. The fifth one is actually not a planet. As Mario walks along, glowing blocks begin to appear, forming a path. This is reminiscent of the Space Junk Galaxy. The sixth is a cylindrical planet resembling a castle where Mario travels through the lava-filled core. This planet has Bullet Bills and Banzai Bills. The last planet is the pathway toward the battle between Mario and Bowser.