Letters credit from Todd Klein via http://kleinletters.com/.
Throughout the story are profiles of villains the gang has encountered before (with the titles of the TV episodes in which they first appeared): the Indian Witch Doctor, the Hawaiian Witch Doctor, the Werewolf, the Giggling Green Ghost, the Telescope Ghost, the Man from Mars, Captain Cutler's Ghost, and the Space Kook. In an homage to the show, Scooby, Shaggy and Velma run past the same background over and over and Velma trips and loses her glasses.