Mattermouths are enemies that are found in Super Mario Galaxy 2. They look like large Dry Bones skulls with

A few Mattermouths in Haunty Halls Galaxy.

glowing yellow eyes. Mattermouths eat the ground, causing holes for Mario to fall through. However, the ground eaten comes back gradually. They cannot be defeated, but if stomped on, they will turn around the other way and keep eating. Mattermouths can be found in places like Bowser's Lava Lair and Haunty Halls Galaxy.