Bowser Jr.'s Fearsome Fleet
Bowser Jr.'s Fearsome Fleet is the last galaxy of World 3 in Super Mario Galaxy 2. Mario fights Megahammer here, a new boss in the game operated by Bowser Jr. in a stage. Hammer Bros. can be found in the pre-boss area. Yoshi is also found in this galaxy; he is essential to the defeat of Megahammer.
 Starting Planet
There are a few Fizzlits in this metallic planet, and two Bullet Bill blasters in the walls. There are some yellow platforms that disappear after a set amount of time. At the end of the planet, there is a glass sphere the player must break by making Yoshi eat Bullet Bills and spit them back out towards them. There will be a yellow and white platform, which the player will ride through the Gunner Path.
 Gunner Path
This path is filled with Undergrunt Gunners and Mines. At the end of the path, the player will need to kill the Fizzlits and flip the switch to continue. The player will need to also break the glass sphere blocking the exit using a Bullet Bill.
 Bullet Bill Planet
There is a Hammer Bro. on this planet, along with several Bullet Bill Blasters. The player will have to break the glass dome covering the lever so they can progress.
This path is much shorter than the Gunner Path, but it's just as dangerous. There are a few mines scattered along the path. During the player's travels, two Airships will appear, one with a ? Block and the other with a Hammer Bro and a Comet Medal. The player will need to shatter the glass sphere at the end of the path to progress.
 Megahammer Planet
This is the planet where the player battles Megahammer. It is shaped like a green and white ring with a few Sling Stars and some black and yellow segments that fall off after Megahammer smashes its hammers against the planet or shoots a Banzai Bill at it. There are also some Star Bits around the top of Megahammer.
 Bowser Jr.'s Mighty Megahammer
The player will land on the Starting Planet. They must find Yoshi and make him eat a Bullet Bill and destroy the glass sphere on the planet. This will unlock a new area on the planet. There are more Fizzlits and a lever. Yoshi must turn the lever to activate a moving platform in order to reach the next planet. While traveling the Gunner Path, there are several Undergrunt Gunners shooting Bullet Bills at the duo and many Mines. When the player and Yoshi reach the second planet two more Fizzlits and another lever and platform await. When the platform is activated, an Undergrunt Gunner, more Mines and another glass ball with Bullet Bill Blasters blocks the player's path. The player must break the ball to reach the Bullet Bill Planet. The lever for this planet is encased in a glass dome that Yoshi must shoot a Bullet Bill at to destroy. Then, when the player activates the platform, two airships - one with a Hammer Bro. - will appear along with one more glass ball with Bullet Bill Blasters. When the ball is shattered, the Luma Shop Planet will be unlocked. When the Launch Star is used, the two will fly to the Megahammer Planet, where Bowser Jr. will appear and attach his Robot Cockpit to the body of Megahammer. In the ensuing battle, Yoshi must swallow Bullet Bills to destroy the three blue domes on Megahammer. This will cause Bowser Jr. to expose the windshield of his Robot Cockpit. Mario must hit the cockpit twice with Bullet Bills to bring the mechanical behemoth down. Mario and Yoshi must use a Sling Star to get the third Grand Star so they can enter World 4.
 Megahammer's Daredevil Bash
The Daredevil Comet must be in orbit in order to select this mission. The player will start out on the Megahammer Planet. He will have to fight Megahammer with only one unit of health. The player will have to use Yoshi to defeat the hammering monster once again.
 Green Star 1
The player will redo the Bowser Jr.'s Mighty Megahammer mission. The first Green Star is located just behind the rightmost Undergrunt Gunner while riding the platform on the Gunner Planet. The player must use Yoshi to grab the Bullet Bill and destroy the Gunner to be able to safely grab the star.
 Green Star 2
The player will redo the Bowser Jr.'s Mighty Megahammer mission. The last Green Star is positioned on the Airship Fleet Path. The player must jump on to the second airship, the one with the Hammer, and carefully manoeuvre on the front plank, and jump off it on to the Star.
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