Complete Monster: Mr. Abney from "Lost Hearts" (link) is a seemingly avuncular and kindly caretaker who takes in his orphaned 11-year-old cousin Stephen. Stephen soon notices the ghosts of a little Gypsy girl and a young Italian boy prowling the grounds, and it is revealed Abney himself is an occultist who wishes to achieve great power. To this end, Abney takes in children and once they hit a certain age, he cuts out and consumes their hearts which also condemns them to fate as lonely specters. Stephen is his next intended victim, and Abney uses his own journals to gloat over how ridiculous the concept that human justice can apply to him is, seeing nothing wrong with sacrificing children for his own benefit.
Nightmare Fuel: Made more effective by James' leaving a lot of room for imagination.