Gina Rodriguez Velma Dinkley (voice) Frank Welker Scooby-Doo / Pterodactyl (voice) Ariana Greenblatt Young Velma (voice) Christina Hendricks Officer Jaffe (voice) Mckenna Grace Young Daphne (voice) Mark Wahlberg Blue Falcon (voice) Zac Efron Fred Jones (voice) Amanda Seyfried Daphne Blake (voice) Henry Winkler Keith (voice) Will Forte Shaggy Rogers (voice) Jason Isaacs Dick Dastardly (voice) Iain Armitage Young Shaggy (voice) Kiersey Clemons Dee Dee Skyes (voice) Ken Jeong Dynomutt, Dog Wonder (voice) Tracy Morgan Captain Caveman (voice) Pierce Gagnon Young Fred (voice) Simon Cowell Himself (voice) John DiMaggio Restaurant Owner (voice) Kevin Heffernan Bike Cop Gary (voice) Maya Erskine Judy Takamoto (voice) Billy West Muttley (voice) Don Messick Muttley (archive audio) (voice) Fred Tatasciore Cerberus (voice) Justina Machado Jamie Rivera (voice) Tony Cervone Ghost / Mr. Rigby / Alice (voice)