Complete Monster/The Haunting Hour the Series


 * The Ax Crazy doctor from the Season 1 Episode "Lights Out". In life, he brutally punished hospital patients who were caught out after 9:PM through means of electric torture and flat-out lobotomies. In death, he haunts the hospital to terrorize both living and the dead there. The other ghosts who dwell in the hospital are still scared shitless of him and are actually trying to protect the teenage protagonists from him! No wonder he's considered by some to be the most evil villain in a R.L Stine story.
 * Jake the Ghost from "The Dead Body". He pretends to offer friendship and emotional support to a bullied boy, but it's all part of a plan to trade their lives so that the boy becomes a ghost while Jake gets to live inside the boy's body. Once inside his body, Jake torments the boy right in front of him, even dating his crush just to spite him! In general, he is depicted as being quite The Sociopath.