Happy Halloween Scooby-Doo! features the familiar voice talents of Frank Welker as Scooby-Doo/Fred Jones, Grey Griffin as Daphne Blake, Matthew Lillard as Shaggy Rogers and Kate Micucci as Velma Dinkley. The film also stars Cassandra Peterson as Elvira, Mistress of the Dark and Bill Nye as himself. Happy Halloween Scooby-Doo! was executive produced by Sam Register (Looney Tunes Cartoons). The film was written, produced and directed by Maxwell Atoms.