The dybbuk is the Jewish version of a demon in its mythos. If you think a run-of-the-mill demon is bad, the dybbuk is much worse. The creature latches itself onto the souls of good, honest people and causes destruction and mayhem wherever it goes.
The thing itself is a broken soul desperately trying to find something to support itself. But the creature never quite knows what is going on and can only cause pandemonium. Unlike other monsters on this list, it doesn’t quite have a physical form, which may only make you even sorrier for the poor thing. Well, as sorry as you can be for a broken soul thrashing people around from within.