Bowser's Galaxy Reactor

"Finally! You got here just in time to see the creation of my galaxy in the center of the universe! WATCH AND WEEP! From this galaxy, I'll rule a great galactic empire with Peach by my side. It will last forever!"

- Bowser

Bowser's Galaxy Reactor is the final galaxy in Super Mario Galaxy. It is located in the center of the universe and can be accessed only by talking to Rosalina on the Comet Observatory. After the player talks to her, she will transform the observatory into a comet and fly it to the center of the universe, destroying some of Bowser's forces along the way.

This is where the final Grand Star is located, and as such features the final battle between Mario and Bowser. During the battle, Bowser Jr. watches from the sidelines on his airship while holding Princess Peach captive. After defeating Bowser, one of the planets near his large sun implodes and turns into a supermassive black hole, causing the entire galaxy to collapse in upon itself, after which it begins to suck up the entire universe, along with Princess Peach's Castle and the Comet Observatory as well. The Lumas all throw themselves into the black hole to reverse its effects and prevent the destruction of the universe. Afterwards, the galaxy is reformed, and Mario, Peach, Bowser, and many others land safely back in the Mushroom Kingdom.

Planets/Areas
NOTE: Unless otherwise noted, all names are unofficial.

Starting Area
This is the first area that Mario encounters after entering the Warp Field inside Peach's Castle. The extensive vertical walls of this strange area appear to be part of a crumbling castle. This particular section of the level contains special Gravity Spotlights which allow Mario to walk directly up the vertical walls when the gravity field of the spotlights is entered. Several Dry Bones also patrol the area, and can trip Mario if he's not careful.

Lava Planet
This planet is the first of three element planets that are encountered one after another. The planet itself is made completely of lava, though it does have multiple steel platforms rising out of the lava, along with moving sections of cooled lava which form moving pathways across the diameter of the planet. The steel platforms on the planet will begin to sink down into the lava as soon as Mario sets foot on them. The only significant obstacles that Mario will face on this planet (aside from the sinking platforms) are Podoboos and steam geysers. A few coins can be found on certain parts of the planet, along with a 1-Up Mushroom. This planet is the one that explodes at the end of the game, creating the black hole that the Lumas stop.

Ice Planet
This planet is similar and seemingly larger than the previous planet Mario visits, except that it is made out of ice instead of lava. It has Ice Blocks that create a path across its frozen surface. The Ice Blocks last for about six seconds before they disappear, meaning that they must be navigated quickly. The ice surface of the planet acts like lava, just like fatally cold water found in Snowman's Land of Super Mario 64.

Sand Planet
This planet also appears to be larger than the previous planet and is the last element planet, but is made of sand. To get across this planet, Mario must follow moving stone paths to avoid Firebars and quicksand that results in instant death. In this sense, it is rather similar to the Lava Planet, as both planets involve a narrow, moving pathway with a deadly substance making up the remainder of the surface and fire-based obstacles. A pair of Galactic Tornadoes can also be found here, although they are of no use to Mario, for they only lead to his doom.

Lava and Water Planets
These are two unreachable planets off to the side of the element planets. One is completely made of water, and the other is made of lava.

Space Junk Area
These are blocks that float around space, but when Mario gets close to them, the glowing blocks begin to appear beneath Mario's feet, which forms a path for him to continue. If Mario stays on the platform too long, it will disappear. He must also deal with alterations in the gravity's direction, and time his movements to avoid Firebars.

Lava 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 using moving and sinking platforms while avoiding all enemies and obstacles with limited cover and a sparse supply of coins. Mario can lure Bullet Bills into Bowser Statues for Coins there. The walls of the planet have their own gravity. There is also a hidden black hole.

Stairway
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 on the left and the right of the stairs. If Mario wishes to get these, he must do it quickly or the path will crumble when Bowser Jr. shoots meteors from his airship.

Bowser's Rock Planet
This is the first planet is where the first stage of the final battle takes place. It has Thorny Flowers growing on the surface. Mario can have Bowser crush the plants to get Star Bits and coins.

Bowser's Shell Planet
This is the second planet where the second stage of the final battle takes place. It has Thorny Flowers and Stretch Plants growing on the surface of it. Mario can have Bowser crush the Thorny Flowers or spin the stretch plants into the Thorny Flowers to get Star Bits or coins.

Galaxy Reactor
This last planet is where the third and final stage of the final battle takes place. It only has coin lamps on the surface, which Mario could shoot Star Bits at to get coins. The reactor is surrounded by a sphere of lava that makes up the massive sun of Bowser's galaxy. The final Grand Star of the game is hidden inside the reactor.

Enemies

 * Dry Bones
 * Firebars
 * Podoboos
 * Galactic Tornadoes
 * Bullet Bills
 * Banzai Bills
 * Thwomps
 * Bowser (boss)

The Fate of the Universe
Mario has to venture through this galaxy until he encounters Bowser. Mario starts on a small, rocky area resembling part of a castle wall. When Mario uses gravity spotlights, he will climb the walls and arrive at a tower being guarded by Dry Bones. At the top, a large Gravity Spotlight sends Mario across to the Lava Planet. He must cross this by utilizing cooled lava sections moving in the opposite direction to him and sinking platforms. A second large spotlight carries Mario to the Ice Planet at the end of the pathway. The surface of the Ice Planet and the Lava Planet both cause one piece of HP loss for Mario if he touches it. The Ice Planet's pathway is formed by Ice Blocks that shoot in from space, but these vanish after a few seconds. The third planet, reached by another spotlight, is made of quicksand, which is fatal if Mario touches it. The planet is traversed by narrow platforms which move across the planet against Mario and dip beneath the planets surface. There are also Firebars in the way. Another spotlight takes Mario into a Space Junkyard where platforms shoot in to form a path and shortly vanish, similar to the ice planet. However, gravity arrows and Firebars provide tough-to-navigate obstacles. At the end of the pathway, a gravity spotlight allows access to the Castle Tower, a hollow, cylindrical planet made entirely of lava, stone and metal. Bullet Bills, Thwomps, Banzai Bills, and the platforms of the area all create a treacherous terrain for Mario. At the end, a Launch Star will take Mario to Bowser's Final Stand.

Bowser Jr. appears on his airship at the bottom of the staircase leading to Bowser with Princess Peach on board. He taunts Mario, then flies behind Bowser and begins shooting down the staircase with meteors. Along the way is a 1-Up Mushroom and a Life Mushroom, but grabbing them takes up valuable time. After Bowser explains his plan, the gravity of a nearby metallic planetoid attracts him and Mario. He transforms into a boulder with his head sticking out of the top. If his head is hit by a Thorny Flower or Mario's spin attack, he will fall out of the boulder, and must be hit again to take damage. When he is hit for a second time, he and Mario will fly to another planetoid. Here, Bowser shoots fireballs which can be blocked by Stretch Plants, and transforms into a ball made of two of his shells. He then rolls around the planet. Mario must Star Spin into sling plants to knock Bowser onto his back, and then use his Star Spin attack on him. After Mario does this twice, he and Bowser will fall towards a giant sun, one of the biggest planets in the game. It is 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 where they are located on a reactor planetoid that resembles a Mario Strikers Charged ball, except for the fact that 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 Mario must obtain. 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 the second planetoid upon which he fought with Mario, on a rocky platform which was sinking into the planet. As its gravity and mass increase, the planet sucks in more and more rocks from around it, then collapses under 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 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 they appear to be destroyed in the process.

Names in other languages

Trivia

 * On the Sand Planet, it is possible for the player to reach the Galactic Tornadoes by long jumping off the moving platform and Star Spinning at the ending height of Mario's long jump. The Galactic Tornadoes do nothing good for the player and can occasionally launch the player into space, making Mario lose a life.
 * When Mario is pulled to the Brown Planet (this is the second planet encountered in the final battle), normally, the player is supposed to wait until Bowser is done launching fireballs from his mouth, and then use the multiple Stretch Plants scattered around the planet to hit Bowser when he curls into a spiky ball and rolls around the planet, thereby causing him to fly helplessly around the planet on his back, and leaving him vulnerable to further attack. However, if the player does not wish to wait for Bowser to finish his fireball attack, they can simply approach Bowser before he rolls into a spiky ball and spin the Stretch Plant nearest him, which will also cause him to fly around the planet on his back, thereby eliminating the need for the player to endure both of his attacks, and creating a shortcut.
 * On the lava planet, if Mario (or Luigi) stands on the edge of the solid rock platform just before the next gravity spotlight beam and go into first person view and looks at the right, the player will be able to see the castle tower where Bowser is standing. Also, if the player slowly moves Mario's (or Luigi's) sight around while looking at the castle tower the player can see a misplaced gravity spotlight beam on the star under the castle tower.
 * Bowser's Galaxy Reactor is the only single-star galaxy to have its own music.