Scariest Thing In All Of Tolkien's Creation...Ever

[Eönwë]

How about Black Númenoreans and Gothmog (both!)

edit: And Morgoth's unnamed creations (but that's probably the same "The 'Nameless Things' Gandalf says live under the earth").

Originally Posted by Lalwendë

1. Eru (yes, he's the boss, and can do anything)

Also, anyone who says that all evil redounds in his glory is definately scary for me!