doppelganger: a ghostly double of a living person that haunts its living counterpart
legendary creature: a monster that is unverifiable but popularly accepted as possibly factual
ketamine: a general anesthetic and tranquilizer (not a barbiturate) that is administered intravenously or intramuscularly; used mainly by veterinarians or for minor surgery with geriatric or pediatric patients; taken in large doses it causes hallucinations similar to those associated with the use of PCP