Mattermouth

Mattermouths are enemies first appear in the game Super Mario Galaxy 2 that resemble the skulls of Dry Bones. They also seem to resemble Bone Dragons. It's name appears to be a pun on "motormouth".

Super Mario Galaxy 2
They are found in places such as the Haunty Halls Galaxy and Bowser's Lava Lair and eat away part of the ground, which regenerates after a few seconds. If Mario falls into the holes in the ground created by the Mattermouths, he will lose a life. Mario cannot destroy them, but he can stop them temporarily by stomping on their heads, which will turn them around and cause them to begin eating the ground in the opposite direction. If Mario is attacked by one of these enemies, he will lose one wedge of his Health Meter.

Mario Party: Island Tour
Mattermouths reappear in Mario Party: Island Tour in the minigame Tragic Carpet Ride. Here they eat up the carpet that the players are standing on while the players try not to fall.