Ungoliant could terrify elves with her presence

But when we urged on our horses they reared and cast us to the ground, and they fled away wild. We lay upon our faces without strength; for suddenly the cloud came on, and for a while we were blind. But it passed us by and moved away north at great speed. Melkor was there, we do not doubt. But not he alone! Some other power was with him, some huge evil: even as it passed it robbed us of all wit and will. 'Darkness and blood! When we could move again we came to the house. There we found the king slain at the door. His head was crushed as with a great mace of iron.