While the gang are solving the mystery of Sir Ruber's ghost, Scooby and Shaggy are transported into the musical version of Quest for Camelot, where they team up with Kayley, Garrett, Devin and Cornwall into retrieving the sword, Excalibur from the evil Sir Ruber.
- Scooby-Doo (Frank Welker) - he and Shaggy are transported into mythological Camelot
- Shaggy Rogers (Matthew Lillard) - he and Scooby are transported into mythological Camelot
- Kayley (Jessalyn Gilsig, Andrea Corr for singing voice) - She has often blended in the Modern world and seeked the Mystery Inc gangs help, she is often seen with Daphne to show her the new fashion and not old fashion.
- Young Kayley (Sarah Rayne)
- Garrett (Cary Elwes, Bryan White for singing voice) - goes by the name "Bruce Conners", who is seen at the end studying a file on the Pokeman.
- Devon (Eric Idle) and Cornwall (Greg Berger, replaces Don Rickles) - Two headed Dragon who acts as a link between the Dragon lords and the humans.
- Ayden (Frank Welker) - a falcon who often drives Scooby nuts.
- Fred Jones (Frank Welker) - he, Daphne and Velma are investigating Ruber's ghost, while Shaggy and Scooby were transported into Camelot. He is used as substitute bait to lure Ruber's ghost
- Daphne Blake (Grey Griffin) - she, Fred and Velma are investigating the Ruber's ghost, while Shaggy and Scooby were transported into Camelot
- Velma Dinkley (Kate Micucci) - she, Daphne and Fred are investigating the Ruber's ghost, while Shaggy and Scooby were transported into Camelot
- Ruber (Gary Oldman) - the film's main antagonist, his goal is to steal Excalibur and take over Camelot. His ghost is what Fred, Daphne and Velma are after
- The Unknown - Ruber's pets, which he uses as spies, weapons and tracking devices
- Griffin (Bronson Pinchot) - the film's secondary antagonist, Ruber's minion and pet
- Bladebeak (Jaleel White) - the film's designated tertiary antagonist, he is a chicken turned into a blade by Ruber as an unwilling antagonist
- Juliana (Jane Seymour, Celine Dion for singing voice) - Kayley's mother, seen in Flashbacks before Kayley's training to become a knight.
- King Arthur (Pierce Brosnan, Steve Perry for singing voice) - Descendant of the original Arthur and head of the agents of Camelot, he kept Camelot safe from outsiders but seems understanding over Scooby and Shaggy.
- Sir Lionel (Gabriel Byrne) - Kayley's father, appears in flashbacks getting killed by Ruber, and training Garrett
- Merlin (Cirian Hinds, replaces John Gielgud) - summons Scooby and the gang through a portal and reveals the secret of Camelot is actually parallel to their verse. He is displeased with Fred's stupidity and Scooby's cowardice.
- Dr. Robert E. Conrad (Gary Oldman) - a scientist, who asks for the gang's help on the Ghost of Sir Ruber haunting him
- General Ranclar (Sean Wright) - The head general of the Beast Unit and Dr. Conrad's rival, Reason: he is similar to Rothbart.
- Orion Balthazar (Liem O'Brien) - Captain of the Dark Prism, Reason: he keeps documents on Camelot's whereabouts.
- Donna Bryce (Pamela Segal) - an Undercover journalist who is seeking info of Camelot when it was cut off from the world, Reason: her sightings in every area of Camelot.
- Herald Grammer (Patrick Warburton) - Dr. Conrad's assistant, Reason: He often is seen keeping documents for Dr. Conrad.
- Gertie Bellwood (Grey DeLisle) - First mate of the Dark Prism, Reason: She is often shady about the Ghost.
- Robert E. Conrad/Ghost of Ruber (Gary Oldman) - Reason: to keep his ancestor from driving him nuts from trying to have him go to Camelot.
- General Ranclar (Sean Wright) - Reason: to steal Merlin's secret enchantments to get his power of the Forbidden Arts.
- United We Stand - ???
- On My Father's Wings - ???
- Ruber - ???
- The Prayer - ???
- I Stand Alone - ???
- If I Didn't Have You - ???
- Looking Through Your Eyes - ???
- I Stand Alone (Reprise) - ???
- Looking Through Your Eyes (LeAnn Rimes) - end credits
- I Stand Alone (Steve Perry) - end credits
- The Prayer (Italian Version) - end credits
- This is a crossover with Quest for Camelot.
- There was a red herring that keeps Conrad from being revealed as Sir Ruber, which is using a device based on Ventriloquism.
- Greg Berger replaces Don Rickles as the voice of Cornwall after his death, while Cirian Hinds replaces John Gielgud as the voice of Merlin.
- This film is dedicated to the memory of Don Rickles and John Gielgud.