Bowser's Galaxy Reactor

Bowser's Galaxy Reactor is the final galaxy 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 Princess Peach. 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.

Castle Wall
This area looks to be as if it is part of a crumbling castle. This part of the level contains Gravity Spotlights that let Mario walk on any solid object the spotlight is facing. Several Dry Bones patrol the area.

Lava Planet
This planet is the first of three element planets. It is made completly of lava with cooled lava and steel platforms.

Ice Planet
This planet is similar and seemingly larger than the lava planet and is the second element planet, but is made out of ice instead of lava. It has ice blocks that create a path a cross its frozen surface. The ice black last for about 6 seconds for it disappears forever. Strangely the ice surface of the planet acts like lava.

Sand Planet
This planet is also semingly larger than the last planet and is the last element planet, but is made of sand. You sink in the sand, unlike when you touch the ice or lava, which get Mario damaged. To get across this planet, Mario must follow stone paths and avoid Firebars.

Cosmic Blocks
These are blocks that float around space, but when Mario gets close to them, the glowing blocks begin to appear beneath the plumber's feet, which forms a path for Mario to continue. If Mario stay too long on the platform, it would disappear.

Tower Planet
This planet is a cylinder resembling a castle tower. Though the inside is walled with lava. This planet has Bullet Bills, Banzai Bills, and Thwomps. Mario must travel to the end to reach the Launch Star.

The Pathway
This is the pathway toward the battle between Mario and Bowser. It consists of a flight of stairs. There are two side platforms that contain a Life Mushroom and a 1-up Mushroom. But if Mario wishes to get these, he must do it quickly because the path will crumble when Bowser Jr. shoots meteors from his airship.

Purple Planet
This first planet where the final battle takes place. It has spikey plants living on the surface. Mario can have Bowser crush the plants to get Star Bits and coins.

Brown Planet
This second planet where the final battle takes place. It has spikey plants and elastic trees living on the surface. Mario can have Bowser crush the plants or spin the trees into the plants to get star bits and coins.

Galaxy Reactor
This last planet where the final battle takes place. It only has coin lamps on the surface, which Mario could shoot Star Bits at the lamps to get coins. The reactor is surrounded by a sphere of lava.

Lava and Water Planets
These are two more unreachable planets of to the side of the element planets. One is completely made of water and the other of Lava. The only way to reach them is by hacking the game.

The Fate of the Universe
The way Mario has to take to reach the battle with Bowser is not an easy one. He starts on a small rock resembling part of a castle wall. Using gravity spotlights, Mario could climb the walls and arrive at a tower guarded by Dry Bones. At the top a large Gravity Spotlight would carry Mario across to the Fire Planet, the path across this was over rocks that would topple over when stepped on, and sinking platforms. A second large spotlight carries Mario to the ice planet at the end of the pathway. Both the ice planet's surface and the fire planet's surface would cause one point of damage if touched. The Ice planet's pathway is formed by ice blocks that shoot in from space, but these would vanish after a time. The third planet, reached by another spotlight, is made of sinking sand, which is fatal if touched. The planet is traversed over circular platforms which move around but dip beneath the planets surface. There were also fire bars in the way. Yet another spotlight would carry Mario into a space junkyard, platforms would shoot in and shortly vanish, like on the ice planet. However, gravity arrows and fire bars get in the way this time. At the end of the pathway, a Gravity spotlight allows access to the fire tunnel, a hollow planet made entirely of fire and is cylindrical. Bullet Bills, sinking platforms, Thowmps and Banzai Bills all get in Mario's way here. At the end, a launch star takes Mario to Bowser's Final Stand. Bowser Jr. appears on his airship at the bottom of the staircase to where Bowser stands with Princess Peach behind him. He taunts Mario, then flies behind his father and begins shooting down the staircase. When a meteor hits the staircase, the piece will crumble and fall. Along the way there are a 1-Up Mushroom and a Life Shroom. Grabbing them takes up valuable time, however. After Bowser explains his plan, the gravity a nearby planetoid made of metal attracts Mario and he. He transforms into a boulder with his head sticking out of the top. If his head is hit by a spiky bush or Marios spin attack, he will fall out of the boulder, then must be spun again to take damage. After he is hurt twice, Mario and Bowser will fly to another planetoid. Here, Bowser transforms into a ball made of two of his shells. He then rolls around the planet. Mario must Star Spin into sling plants to hit Bowser on his back, then the player has to Star Spin him. After doing this twice, Mario and Bowser will fall towards a giant Sun, one of the biggest in the game. It is, however, hollow, with holes, and the two combatants will fall through one of these to land on the reactor at the center. Here, Mario fights Bowser in a similar way to how he does in Bowser's Star Reactor and Bowser's Dark Matter Plant:in a planetoid that remembers a Mario Strikers Charged ball; except Bowser has the attack he used on the second planetoid, which Mario can only avoid. After hitting Bowser twice, Bowser will fall out of the reactor's gravity field and into the Sun. A Grand Star will then be revealed from inside the reactor, which the player takes. As Mario flies away with the Grand Star, Bowser Jr.'s airship plummets towards the Sun, but Mario rescues Princess Peach and flies her to the area where he first entered the Galaxy. It is then revealed that Bowser has survived his fall into the gigantic Sun, but is stranded on a smaller one, on a platform which is sinking into the planet. As its gravity increases, the Sun sucks in more and more rocks from around it, then collapses on its own weight, becoming a giant Black Hole. It begins to suck up everything around it including Mario, Peach, Bowser's Airship Fleet, Peach's Castle, and the Comet Observatory. It would appear that everything is lost until Mario's (or Luigi's) Luma pops out, waves its arm and zooms toward the black hole. It is soon joined by all of the other Lumas. The Lumas twist the Black Hole into oblivion, but appear to be destroyed in the process.

Trivia

 * On the planetoid made of sand the player can reach the Tweesters by long jumping off the moving platform and Star Spinning at the ending height of Mario's long jump. The Tweesters do nothing good for the player and they occasionally launch the player into space, making Mario lose a life.
 * An upside-down "L" made out of Star Bits appears on the wall of one of the platforms.
 * On the lava planet if Mario (or Luigi) stands on the edge of the solid rock platform just right before the next gravity spotlight beam and go into first person view and look at the right, the player will be able to see the castle tower where Bowser is standing on. Also, if the player slowly move Mario's (or Luigi's) sight around while looking at the castle tower the player can see a missplaced gravity spotlight beam on the star under the castle tower.