Mindy Cohn Velma Dinkley (voice) Grey DeLisle Daphne Blake (voice) Frank Welker Scooby-Doo / Fred Jones (voice) Matthew Lillard Shaggy (voice) Danica McKellar Madelyn Dinkley (voice) James Patrick Stuart Whirlen Merlin (voice) Crystal Scales Crystal (voice) Brian Posehn Marlon Whirlen (voice) Jeffrey Tambor Mr. Calvin Curdles (voice) Diane Delano Mrs. Alma Rumblebuns (voice) John DiMaggio Groundskeeper Amos (voice) Melique Berger Upset Mother (voice) John Stephenson The Sheriff (voice) Dee Bradley Baker Sherman (voice) Olivia Hack Treena (voice) Dave Attell GPS (voice)