Thwomp

Thwomp are animate cinder-blocks found mostly in the Mushroom Kingdom in every Mario series.

Character description
Thwomps make their debut appearance in Super Mario Bros. 3. They usually try to squish Mario under their weight whenever he passes beneath them. Thwomps are possible to be easily avoided by using the Statue Mario ability. With this, it is impossible for Thwomps to destroy Mario by crashing him from above. They return in the game's remakes, Super Mario All-Stars and Super Mario Advance 4: Super Mario Bros. 3 in the same fashion as the older Thwomps. They feature improved graphics and retake their especially mad expressions. Curiously, these Thwomps have a "bigger spike" on top of their forehead, separated from the rest of the body by what looks like a small ribbon of sorts. This spike is prominent in appearance but has no effect in the game. It is also worth noting that these Thwomps, instead of having their eyes separated, have both eyes as glowing dots in a black space. This is most likely due to palette and space limitations.

In Super Smash Flash 2
In Super Smash Flash 2, Thwomp appears on Bowser's Castle as a hazard; they will randomly fall at high speed towards them and smash the platforms. The player can give a serious damage when he falls downward.