Bonefin Galaxy

The Bonefin Galaxy is a galaxy in Super Mario Galaxy. This galaxy, like the Drip Drop Galaxy, is basically a large body of water with a solid core. Unlike the Drip Drop Galaxy, this galaxy has a large, spiky, shell shielding most of it. This galaxy is the home of Kingfin, who Mario must defeat to earn a Power Star.

To unlock this Galaxy, the player must have at least 55 stars and have the Drip Drop Galaxy completed.

Kingfin Planet
This is a large planet with a very large body of water. The planet is surrouned by a spiky shell. Kingfin and his followers live here. There is a 1-Up Mushroom inside a glowing green treasure chest and a Life Mushroom hidden in some rocks.

Starshroom
When Mario starts the galaxy, he will start out on a green Starshroom near the Kingfin planet. There are several Star Bits on its underside, and a launch star on the top of it will take Mario to the Kingfin planet.

Kingfin's Fearsome Waters
In the first and only level, Mario must defeat Kingfin by attacking with Koopa Shells. After Kingfin takes one hit, he will start releasing robotic fish that will home in on Mario's position. Once Kingfin has been hit five times, he will crumble, die, and release a Power Star.

Trivia

 * The Bonefin Galaxy is the only bonus galaxy in Super Mario Galaxy in which Mario must fight a boss.