I would go with a hint of mystery. Mysterious things are usually the creepiest. Imagine a human body. It looks perfectly normal, except there is something different about it. read more
If I had to pick just ONE thing most shared among creepy REAL things, it would be teeth, fangs, claws, stingers or other similar features which would bite, tear, shred, or penetrate. Considering only imaginary creepy things, what is most shared is wetness, slime, or moisture. read more