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. Also, Yoshi can be found in this galaxy as well, considering that he is needed to defeat the mechanical giant.

First Platform Planet
There are a few enemies in this metallic planet, and two Bullet Bill blasters in the walls. At the end of the planet is a crystal Mario must break by making Yoshi eat Bullet Bills, and a big platform that takes Mario through some enemies that shoot more Bullet Bills at him.

Second Platform Planet
There is a Hammer Bro. in this planet, along with several Bullet Bill Blasters. After getting on a platform, Mario and Yoshi will have to avoid obstacles such as airships and Bullet Bills. The Comet Medal can be found on the second airship.

Megahammer Planet
This is the planet where Mario battles Megahammer. It is shaped like a ring with a few Sling Stars and some black and yellow segments that fall off after Megahammer smashes its hammers against the planet.

Megahammer's Daredevil Bash
The player will land on the Megahammer Planet. Then he or she will have to fight Megahammer with only one life. The player will have to use Yoshi to defeat the hammering monster once again.

Green Star 1
The first Green Star is located just behind the rightmost Bullet Bill Blaster while riding the 2nd platform on the First Platform Planet. The player must use Yoshi to grab the bullet and destroy the Bullet Bill Blaster to be able to safely grab the star.

Green Star 2
The last Green Star is positioned at the Second Platform Planet. The player must guide Mario to the front of the second airship and carefully maneuver him on the front plank, and jump off of it onto the star.

Trivia

 * This is the only Galaxy where Yoshi can be in the Grand Star victory pose.