I'm sure there is a word to describe these, but I do not know what it is. These are a particular brand of bad guys. They are scary creatures. You hope they are not real, but secretly fear they might be. My three favorite scary creatures from literature:
3. Dementors, from the Harry Potter series by J.K. Rowling.
Fans of Harry Potter, either the books or the movies, know about Dementors. These are wraith like creatures which feed off human joy, sucking out happiness and hope until only misery and depression and bad memories are left. They are used to guard Azkaban, the prison for the baddest of the bad, in the world of Harry Potter. I always thought that was an unwise decision, as it didn't exactly encourage repentance or positive change.
2. Misery Eels, from Sarah Prineas's The Magic Thief series.
Misery eels are slithery shadowy creatures which thrive off of and intensify fear, loneliness and misery. They can be repelled by light. I'm reasonably certain I ran into a few of these in my childhood, years before these books were written, as the night creatures of my childhood were also slithery-shadowy and were chased away by light.
1. Echthroi, from Madeleine L'Engle's A Wind in the Door and A Swiftly Tilting Planet.
Okay, these guys have to take my number one spot. First, the word is even fun to say: echthroi! It sounds like something caught in your throat you desperately want to get out of your system. And the Echthroi in these two books are not things you want inside you, either. The sole purpose of the Echthroi (from a Greek word meaning "enemy") is to destroy, extinguish, annihilate, all joy, all happiness, all life and beauty, every single thing that is good in the universe. They have no bodies of their own but can be recognized by their foul decaying stench and a cold clammy feeling. They cannot be fought with anger or hatred, as those feelings only give them strength. They can be fought only with love, pure, unconditional love for all, even the unlovable, and by "naming" or affirming the essential nature of every being great or small. That's it in a nutshell, although my summation falls somewhat short.
If you like your evil vague and not completely defined, stay away from these books. If you like your evil to be obvious from the moment they walk into the room, from the moment you hear or read their names, Dementors, Misery Eels, and Echthroi are for you. Don't say I didn't warn you. Remember the power of Love, and make sure your flashlight is working.