Re: The shadow!
Assuming we are basing our idea of the "devil" on Christian theology, as he most often is, then he is not omniscient. The devil is able to feed our minds with ideas and temptations, but unable to know what we are thinking. He is no doubt the greatest schemer ever, but to prevent me from simply turning on a light or walking out into the sun no doubt requires an alteration of reality on some level.
Edit: Shut the fuck up, RNB.