Bone Thwomp

A Bone Thwomp is a species of Thwomp that resembles a large bone inside Bowser. So far, Bone Thwomps have only appeared in Mario & Luigi: Bowser's Inside Story in the Pump Works in Bowser's Body. It is more of an obstacle than an enemy. It rises when Bowser drinks water, and falls when Bowser stops drinking water.

Trivia

 * Bone Thwomps and Chombones may be related.