Kazuo Umezu tends to create pretty creepy stuff however I always felt his stuff borderlined on ridiculous. Regardless, I still enjoyed Drifting Classroom.
I guess when it comes to me, I find realism to be much scarier than ghosts or monsters. When it comes to the thing that scared me the most, it was a photo of an actual baby with a very rare skin disorder. I am not going to put what it is because I don't want to traumatize people.