Undergrunt

Undergrunts are mole-like creatures that appear in Super Mario Galaxy and Super Mario Galaxy 2.

Super Mario Galaxy
In Super Mario Galaxy, Undergrunts appear in Gusty Garden Galaxy in the mission, "The Dirty Tricks of Major Burrows" as uncommon enemies on two planets. Mario cannot do anything to the Undergrunts while they are tunneling underground. But defeat them by ground pounding the ground close for them to pop out. Then Mario must spin the Undergrunts while they're still out of the ground.

At the end of that level, there is a boss extremely similar to an Undergrunt in appearance, Major Burrows, can be defeated in the exact same way.

Super Mario Galaxy 2
Only three undergrunts appear in Super Mario Galaxy 2 on one planet in Battle Belt Galaxy. They are defeated in the same way as in the previous game.

In addition, Major Burrows appears again in Boss Blitz Galaxy.

Appearance
An Undergrunt's appearance is similar to most mole like characters (Monty Moles, Rocky Wrenches etc.). They have dark brown fur, and light brown bellies, noses, and cheeks. Undergrunts also have yellow spiked helmets preventing the player from stomping or spinning the mole. This is the only indication of an undergrunt beside the fact that they leave a dirt trail behind when they tunnel in the ground.

Trivia

 * Besides the helmet, Undergrunts have the exact same appearance of a Rocky Wrench.