Nightmare - Equine ghost of a friendly female horse who costarred with Casper the Friendly Ghost in his many theatrical and TV cartoons. Nightmare's other ghostly friends are Spooky the Tuff Little Ghost, Casper's buddy; The Ghostly Trio  (Stretch, Fatso & Stinkie) who enjoyed scaring people; and Wendy the Witch who first appeared in Casper the Friendly Ghost #20, May 1954 (one month after the first appearance of Nightmare the horse).