A Thwomp is an enemy in most Mario games. It floats in the air, and after a while, it crashes into the ground. In Mario Kart, it does the same to crush or stop racers. It is stone, and when it frowns, it comes down.
Thwomps appeared in each Bowser Castle track. These Thwomps are the first to not feature spikes. They became "active" on the second lap. Blinking Thwomps appeared on Rainbow Road. These unique Thwomps caused racers to spin out on contact, as if they are using a star.
These Thwomps were based on their appearances in Super Mario 64, and were only seen once. They could make racers going at a high enough speed spin out.
Thwomps appear in Bowser's Castle. They are much bigger than their previous incarnations. These become standard in the following games.Bowser's Castle, the N64 version of Bowser's Castle (Marty is no longer green), and the GBA version of Bowser Castle 3. A giant one appears at Thwomp Desert along with some regular ones who are buried in the sand.