Thwimp

The Thwimp is a tiny version of the fabled Thwomp monster which first appeared in Super Mario Bros. 3 but later appeared in The Legend of Zelda series with Link's Awakening and the Oracle series. These creatures will hug the ceiling and slam down to the ground right before you step under them. It is best to only get close enough for them to fall, and as they make their ascent, run past them. The Pegasus Boots allow you to dash under them as well.