Bowser Jr.'s Lava Reactor is the fifth boss galaxy in Super Mario Galaxy. It is located in the Engine Room. To unlock this galaxy, one must get 45 Power Stars. This galaxy is made up almost entirely of a large sun made out of Lava with very few rocks on it. The galaxy also features green hexagonal platforms that sink into the Lava with the player's weight. Bowser Jr. summons King Kaliente to fight Mario/Luigi for the second time (the first first was in the Good Egg Galaxy). When King Kaliente is defeated, Mario/Luigi is awarded with a Grand Star and the Garden is unlocked on the Comet Observatory.
Starting PlanetThis planet is small and is made of dirt. More than half of the planet is gone, for a Black Hole in the center of it is eating it away. There are several Goombas on this planet as well as a Bill Blaster and a glass cage covering a Launch Star. Yep, there's a glass cage with a Launch Star so you know what that means? It means Mario/Luigi must get a Bullet Bill fired from the Bill Blaster to spot him then trick it into hitting the glass cage. This task can be difficult due to the gaps on the planet thanks to the Black Hole, as well as the Goombas on this planet. Anyway, once the Launch Star is freed, Mario/Luigi can use it to blast to the Lava Reactor.
Lava ReactorThis planet is a large sun that is made entirely of lava. There are several green hexagonal platforms that sink into the Lava with Mario/Luigi's weight in a circle on the northernmost part of the planet and some more sinking platforms forming a path on the southernmost part of the planet. This planet is home to King Kaliente and is where Mario fights him for the second time (on the northernmost part of the planet).
King Kaliente's Spicy ReturnMario/Luigi begin on the Starting Planet. This planet is being eaten away by a Black Hole, which creates several gaps Mario/Luigi must jump over just to get from point A to point B. Despite this planet being almost eaten away completely, several Goombas and a Bill Blaster inhabit this planet. There is also a glass cage covering a Launch Star at the end. So, with that being said, Mario/Luigi must get a Bullet Bill fired from the Bill Blaster to notice him and then have it chase him to the glass cage. When the Bullet Bill gets near the cage, Mario/Luigi should go around it so that the Bullet Bill is tricked into hitting the glass cage, causing it to shatter. Once this happens, Mario/Luigi can use the Launch Star to blast him to the Lava Reactor. Here, Mario/Luigi must quickly cross a path of green hexagonal platforms that sink into the Lava with their weight. On the final green hexagonal platform some Octopuses will appear in the Lava ahead and shoot Coconuts at Mario/Luigi. Mario/Luigi should quickly defeat this while avoiding the platforms sinking into the Lava. To avoid falling into the Lava, Mario/Luigi should frequently change platforms. Anyway, once the Octopuses are defeated, Mario/Luigi can use the Launch Star that appears to be blasted to the north side of the planet. He will land on a green hexagonal platform where Bowser Jr. taunts him and summons King Kaliente to fight him. This King Kaliente is much stronger and darker in color than in his first appearance in the Good Egg Galaxy. Anyway, the player must Spin Coconuts that King Kaliente occasionally shoots at Mario/Luigi once to knock off his crown, then three more times to defeat him for good. However, Mario/Luigi must also dodge the Fireballs King Kaliente shoots as well as the Lava Bouncers he summons and the sinking hexagonal platforms that serve as the only platforms to use during the battle. So, Mario/Luigi must frequently change platforms while spinning Coconuts at King Kaliente to defeat him. Once King Kaliente is defeated, Mario can collect the Grand Star, which unlocks the Garden on the Comet Observatory. This is also the final battle before Bowser Jr. is defeated for good, though he reappears in the next boss galaxy, however, he is not fought and instead tries to make it difficult to reach Bowser.
- Starting Planet
- Lava Reactor
- It is possible to collect all 60 Power Stars and defeat Bowser for the final time without receiving the Grand Star in this mission.
- If the player Triple Jumps onto the glass cage covering the Launch Star and Spin they will end up on the Lava Reactor. However, since the player will land nowhere near the path of green hexagonal platforms on the southernmost planet nor the other side, they will have no choice but to fall into the Lava and die after three hits on the lava (because the player bounces in the air when they touch Lava and Lava takes three hits to defeat the player).