Bowser's Galaxy Reactor is the sixth and final boss galaxy in Super Mario Galaxy. It is located at the center of the universe and cannot be accessed from any room in the Comet Observatory. It is unlocked by getting 60 Power Stars as well as the Grand Star in Bowser's Dark Matter Plant. After talking to Rosalina on the Comet Observatory, she will transform the hub into a comet and fly towards the center of the universe, destroying some of Bowser's obstacles in the way. This galaxy is where the final Grand Star is located and is also where Mario/Luigi fights Bowser for the final time. Bowser Jr. watches the battle from his Airship while holding Princess Peach captive. After defeating Bowser, Bowser's large sun shrinks and transforms into a large Black Hole that begins sucking up everything including Princess Peach's Castle and the Comet Observatory as well. The Lumas all throw themselves into the Black Hole to reverse its effects and save the universe from destruction, however, they die in the process. Afterwards, Mario/Luigi, Peach, Bowser and many others land safely on the Mushroom Kingdom.
Starting PlanetThis is the first planet in the galaxy. Mario/Luigi is automatically transferred here when the Comet Observatory heads for the "center of the universe". The walls on this planet appear to be part of a crumbling castle. This planet features the first Gravity Spotlight in the galaxy (and the game itself). These Spotlights allow Mario/Luigi to walk directly on the walls of this planet when their gravity field is entered. Several Dry Bones are also found on this planet and can make Mario/Luigi trip if he is not careful. There is a Gravity Spotlight that will take Mario/Luigi to the Lava Planet at the end of this planet.
Lava PlanetThis planet is the first of the three element planets in this galaxy that appear one after another. This planet is made completely of Lava though it also has multiple steel platforms that rise out of it, along with moving sections of cooled lava which form moving pathways across the planet's diameter. These steel platforms on this planet will sink with Mario's/Luigi's weight. If they are not careful, the player will find himself bouncing on the surface of the Lava Planet if a steel platform sinks completely into the Lava. There are also some Podoboos and Lava Geysers. A few Coins can be found on certain parts of the planet along with a 1-Up Mushroom. Another Gravity Spotlight awaits at the end of the level; it will take the player to the Ice Planet when its gravity field is entered.
Ice PlanetThis planet is similar to but larger than the Lava Planet. However, it is made completely of ice instead of Lava. There are several pieces of ice above the planet, which, similar to Space Junk found in the Space Junk Galaxy and further on in this galaxy, will form a path when Mario/Luigi gets near them. These ice platforms last a few seconds before disappearing, meaning players must be quick to cross these platforms. If not, they will end up falling onto the surface of this planet, which strangely, acts as if Mario touched Lava instead of ice or Freezing Water. That means, after three hits on the planet's surface, Mario/Luigi will lose a life. As shown in the picture to the left <---, there is a 1-Up Mushroom that appears above a high ice platform when it forms. Anyway, at the end of this planet, there is a Gravity Spotlight which will take Mario/Luigi to the Sand Planet.
Sand PlanetThis planet is final planet of the three element planets and is the largest one as well. It is made of Quicksand, which will instantly kill Mario/Luigi if they fall into it. To get across this planet, Mario/Luigi must follow moving stone paths while avoiding the Firebars on this planet and the Quicksand below. Because of this, it is similar to the Lava Planet since both require Mario/Luigi to follow moving paths across a dangerous element that results in death if touched, as well as having to dodge fire-based obstacles and enemies. A pair of Galactic Tornadoes are found here, but they are useless and will only make Mario/Luigi fall to his doom if used. Another Gravity Spotlight is here which will take Mario/Luigi to the Cosmic Platforms Area.
Lava and Water Planets
These are two inaccessible planets that are set off to the side of the element planets. One is made completely of water and the other is made completely of lava.
Cosmic Platforms AreaThis is an area made completely of Cosmic Platforms, which is another name for Space Junk. They are found floating in Space but will create a path when Mario/Luigi come close. However, if Mario/Luigi stands on them for too long, they will disappear, resulting in him falling in Space and losing a life. Mario must also navigate through a section of Gravity Walls while still crossing the Space Junk. Some Firebars are here, which means the player should time their jumps to avoid hitting them. The final Gravity Spotlight in the galaxy (and game) is at the end of this planet, allowing Mario to access the Tower Planet when its gravity field is entered.
Tower PlanetThis planet is a cylinder-shaped planet resembling a castle tower, however, the inside is walled with Lava. This planet is full of obstacles and enemies, including Bullet Bills, Banzai Bills and Thwomps. Mario must travel to the end while avoiding all these enemies in order to reach a Launch Star that will take them to The Pathway. However, this isn't as easy as it sounds. Besides the numerous enemies here, there are also moving and sinking platforms, and little areas to take cover from the Banzai Bills that block Mario's/Luigi's path as they come close. There is also a scarce number of Coins here. However, Mario can lure Bullet Bills into the many harmless Gray Bowser Statues for Coins. It is to note that the walls of this planet have their own gravity.
The PathwayThis is the pathway towards the final battle against Bowser. It consists of a flight of stairs. Bowser's sun can be seen in the background. Anyway, there are two side platforms: the one on the left contains a Life Mushroom and the one on the right contains a 1-Up Mushroom. However, after a certain point on this pathway, Bowser Jr. begins to fire Meteors at the planet, which will destroy it. With that being said, Mario/Luigi must quickly collect the Mushrooms if needed and make it to Bowser, otherwise they will fall in Space and lose a life.
Purple PlanetThis is the first planet where the first portion of the battle against Bowser takes place. It is a small purplish-gray planet. There are Spiky Plants. Bowser has the ability to transform into a Boulder with his head sticking out. Mario/Luigi must Spin his head or have him roll over a Spiky Plant to not only release Star Bits and Coins, but to make him come out of his Boulder form. Mario/Luigi must then Spin him to damage him. Mario/Luigi must Spin Bowser twice when Bowser is at this form to have the two be taken with gravitational force to the Brown Planet, where the second portion of the battle with Bowser takes place.
Brown PlanetThis is the second planet where the second portion of the battle against Bowser takes place. It is a small brown dirt planet. It has Spiky Plants and Stretch Plants growing on its surface. Some Item Crystals with Coins trapped inside can also be found on this planet. Here, Bowser transforms into two duplicates of his shell and rolls around the planet. Using the nearby Stretch Plants, Mario/Luigi can Spin one at Bowser to send him rolling on his back. Mario/Luigi must then Spin him to damage him. Doing this once more will allow Mario/Luigi and Bowser to come to the final planet, the Galaxy Reactor.
Galaxy ReactorThis is the final planet where the third and final portion of the battle against Bowser takes place. There are several yellow orbs on the planet which Mario/Luigi can shoot Star Bits at via the Star Cursor for one Coin. The Grand Star is hidden inside this reactor. The battle here is the same as from the previous two galaxies. Therefore, Mario/Luigi must get Bowser to Ground Pound the blue orbs on this planet, causing Lava to erupt and burn his tail. Bowser then runs frantically around the planet in pain. At this time, Mario/Luigi must Spin Bowser to cause him to spin around the planet on his shell. They must then Spin Bowser again to damage him. Doing this technique again will cause Bowser to be defeated for good and when we say for good, we don't mean only for this galaxy, but FOR THE REST OF THE GAME!!!
The Fate of the UniverseMario/Luigi must collect 60 Power Stars and talk to Rosalina on the Comet Observatory to cause the Comet Observatory to turn into a comet and enter this galaxy. Mario/Luigi start on the Starting Planet which resembles a rocky version of a castle wall. Using the Gravity Spotlights here, Mario must climb the walls here and arrive at a tower guarded by a Dry Bones. At the top, there is another Gravity Spotlight that sends Mario/Luigi to the Lava Planet. Here, Mario/Luigi must cross this planet by utilizing the cooled lava platforms moving towards him and sinking platforms while avoiding Podoboos and other obstacles. At the end, there is a Gravity Spotlight that will take Mario/Luigi to the Ice Planet. Here, some floating pieces of ice will create paths for Mario/Luigi to navigate, however, these platforms will disappear after a while. If the player is still on one of these platforms when it disappears, they will touch the surface of the Ice Planet, causing them to lose a life after three hits. This is because the surface of the planet, despite being made of ice, has the same effect when touched as if Mario/Luigi touched Lava. Another Gravity Spotlight is at the end of this planet, which will take the player to the Sand Planet once its gravity field is entered. On this planet, Mario/Luigi must safely make their way to the next Gravity Spotlight in a similar manner to when they were on the Lava Planet. That is because Mario must navigate along moving stone platforms while avoiding Firebars, as well as the Quicksand below, which can kill him in one touch if accidentally fallen into. Mario/Luigi can then use the Gravity Spotlight at the end to reach the Cosmic Platforms Area. Here, Mario/Luigi will navigate through this planet in a similar manner to the Ice Planet they were on previously. Some Space Junk (also known as Cosmic Platforms) will create platforms for Mario/Luigi to cross as well as walls for them to Wall-Jump up and ceilings for them to walk on when in the Gravity Wall part of this area. Soon, Mario/Luigi must continue to follow these platforms, however, Gravity Walls will appear and drag him in the direction its arrow is pointing at. Some Firebars are in this area as well. Mario/Luigi must be careful to cross this area without hitting the Firebars to safely reach the final Gravity Spotlight in the galaxy (and in the game), however, he must also be quick for Space Junk will disappear after a short while, causing anyone standing on it at that time to fall into Space and die. The Gravity Spotlight at the end will take Mario/Luigi to the Tower Planet. This cylinder-shaped planet is filled with obstacles and enemies Mario/Luigi must avoid in order to reach the Launch Star at the end. Mario/Luigi must cross moving and sinking platforms, hide behind objects to avoid Banzai Bills blocking his path, and use the scarce amount of Coins to survive here. Besides Banzai Bills, there are also Bullet Bills and Thwomps that will make getting to the other side much more difficult than it looks. If the player is low on health, they can lure a Bullet Bill into one of the immobile (and harmless) Gray Bowser Statues to destroy them for one Coin, which can be used to add another wedge to the player's Health Meter. Anyway, once the Launch Star is reached at the end of this planet, it can be used to fly to The Pathway. This planet is nothing but a long path leading to a flight of stairs. There is a Life Mushroom on the platform to the left and a 1-Up Mushroom to the right which can be reached if needed. When climbing these stairs, Bowser Jr. will begin to fire Meteors at the stairs from his Airship, destroying them in the process. Mario/Luigi must quickly climb these stairs to avoid falling into Space below. At the top, Bowser tells Mario/Luigi about his plans to rule the universe with Princess Peach by his side before using gravitational force to send the two to the Purple Planet. On this planet, there is nothing to take notice of besides the Spiky Plants here, which can harm the player if touched. Bowser will transform into a Boulder with his head sticking out. Mario/Luigi must Spin Bowser's head or have him roll over a Spiky Plant to cause him to come out of his Boulder form. Mario/Luigi can then Spin Bowser again to damage him. Doing this process all over again will cause Bowser to use gravitational force to send the two to the Brown Planet where part 2 of the battle takes place. Here, Bowser transforms into two of his spiked shells and rolls around the planet. Mario/Luigi must then Spin a nearby Stretch Plant into Bowser to have him roll on his back around the planet. Mario/Luigi must then Spin him again to damage him. Doing this process once more will cause a hole to appear in Bowser's sun, where the two are then taken to the Galaxy Reactor in the center of Bowser's sun. There are also some Item Crystals covering Coins on the Brown Planet that can be shattered with the Spin if the player is running low on health. Anyway on the Galaxy Reactor, the battle is much similar to in Bowser's Star Reactor and Bowser's Dark Matter Plant, however, Bowser now rolls around the planet. Anyway, Mario must get Bowser to Ground Pound one of the blue orbs on the planet to cause Lava to erupt and burn his tail. Bowser will run around the planet in pain. Using this as an advantage, Mario/Luigi must Spin Bowser to have him spin around the planet on his back. After Spinning him again, Bowser takes damage. Doing this process once more will cause Bowser to be defeated for good. Bowser falls out of his reactor field and into his sun. A Grand Star is revealed which Mario/Luigi can collect to end the mission. Afterwards a cutscene appears showing Mario/Luigi flying away. Bowser Jr.'s Airship gets sucked towards the sun. Mario/Luigi rescues Peach and flies her to the area where he first entered the galaxy. It is then revealed that Bowser survived his fall and in fact, fell onto the Brown Planet. He is stranded on a rocky platform on this planet which was sinking into the planet. As its gravity and mass increases, the planet sucks in more and more rocks before exploding into a giant Black Hole and begins to suck everything up including Mario/Luigi, Peach, Bowser's Airship Fleet, Princess Peach's Castle and even the Comet Observatory. It is seemed as if Mario/Luigi has lost everything, until Luma pops out of his cap, waves goodbye and zooms toward the Black Hole. All the other Lumas follow Luma into the Black Hole. The Lumas then turn everything back to normal before Bowser took over, however, they are killed in the process. Unlike in Bowser's Galaxy Generator of Super Mario Galaxy 2, Luigi (if playing as Mario) is not unlocked and able to be played as by completing this galaxy. Mario must receive all 120 Power Stars in the game. In Bowser's Galaxy Generator, the ability to play as Luigi whenever is unlocked after getting the Grand Star in that mission, causing Luigi to spawn on Starship Mario. In this game, it is different.
- Starting Planet
- Lava Planet
- Ice Planet
- Sand Planet
- Cosmic Platforms Area
- Tower Planet
- The Pathway
- Purple Planet
- Brown Planet
- Galaxy Reactor
- This is the only non-Hungry Luma galaxy in the game to not have a galaxy icon. The Hungry Luma galaxies include the Sweet Sweet Galaxy, Boo's Boneyard Galaxy, Sling Pod Galaxy, Drip Drop Galaxy, Bigmouth Galaxy, Sand Spiral Galaxy and Snow Cap Galaxy.
- On the Sand Planet, it is possible to reach the Galactic Tornadoes by Long-Jumping off the moving platform and Spinning. The Galactic Tornadoes are useless however, and some can propel Mario into Space causing him to lose a life.
- Bowser's fireball breathing and rolling attack can be skipped on the Brown Planet if the player Spins a Stretch Plant into him, causing him to roll on his back.
- On the Lava Planet, if Mario/Luigi stands on the edge of the solid rock platform just before the next Gravity Spotlight and goes into first-person view and looks to the right, the player will be able to see The Pathway where Bowser is standing. Also, if Mario/Luigi slightly moves the camera around the The Pathway, they will see a misplaced Gravity Spotlight on the star under it.