Thwomp Mario is one of Mario's Power-Ups after getting the Thwomp Mushroom that turns Mario into a Thwomp. This transformation is considered as a "companion" ability to Whomp Mario. It makes it's appearance in New Super Mario Bros. VR.
Thwomp Mario can float a jumping height above ground and stomp just about any enemy in one shot. Mario will still loose the Thwomp ability once he hits an enemy, although on less on purpose, it is pretty hard to die from an abyss with Thwomp Mario.