The Thwomp is an enemy in Super Mario Maker. It cannot be eliminated by any means other than falling out of the level or touching it with the Super Star or the Big Mushroom. A Super Mushroom can be applied to make it into a larger Thwomp.
Trampolines, P-Switches or POW Blocks can be kicked up into the Thwomp to halt its fall. If it falls onto an enemy, the enemy is eliminated and the Thwomp keeps falling, and if it falls onto a Brick Block, the fall is slowed and the Brick is destroyed. If it falls onto a Note Block, it continues to bounce until something that halts the fall gets in the way. A good use for the Thwomp is to force Mario to run.