Gobblegut

Gobblegut is a boss in Super Mario Galaxy 2. He is a dragon, who encircles a small planet in Bowser Jr.'s Fiery Flotilla, burrowing into and emerging out of it, in "Gobblegut's Aching Belly".

Appearance
Gobblegut resembles a giant serpentine dragon with a row of numerous red ulcers growing from his body. His scales have beautiful swirl designs and his underside lacks any scales thus exposing his pink skin. Gobblegut has a few jagged rocks protruding from his head and he has a large bulbous chin that has numerous scars on it (most likely due to the numerous times he slams his chin into solid rock).

After becoming Fire Gobblegut, his scales change from light green to lava red, and his skin changes to orange. He also releases lava and fire from his skin and the stones on his body have become orange. However, his ulcers remain unchanged.

Strategy
The red spots surrounding Gobblegut's body can be damaged when Mario jumps over them or uses a Spinning attack. After several hits, Gobblegut becomes angrier, and is always seen making sounds like train whistles with his nose. After the last red spot gets damaged, Gobblegut slows down and explodes, releasing a Grand Star.

The player faces Gobblegut twice, with the second fight being under the Speedy Comet conditions.

Fire Gobblegut
A fire version of Gobblegut is fought as a secret boss at the Battle Belt Galaxy. This Gobblegut is much tougher, as he'll leave behind lava pools when biting into the battlefield. He'll also spit fireballs at times to make it harder for the player.

Trivia

 * The Wiggler boss in Super Mario Sunshine acts similarly to Gobblegut, getting angrier and making train noises every time it gets hit.