Thwomp'd

Thwomps are covered in spikes and anger.

Thwomps can move in one direction, and the opposite of that direction at a slower pace.

Thwomps aim for where Mario is, not where he's going to be.

Thwomps are invincible except for when they're not, like in Mario 3 sometimes.

Thwomps, as mentioned previously, can be killed by 2 out of 3 special suits in Mario 3. Ironically, the frog suit couldn't harm a fly.