Summer's over, and the Mystery Inc. gang return to school in Crystal Cove, unaware of the mysteries their parents and authorities in their town knew what they were doing, but the gang find a secret mystery concerning an original Mystery Incorporated and secret weapons, that will change everything in the final chapter of the Scooby-Doo series.
This movie is dedicated to the loving memory of Casey Kasem, who died in 2014.
August ???, 2018
- Mystery Incorporated:
- Scooby-Doo (Frank Welker)
- Shaggy Rogers (Matthew Lillard)
- Fred Chiles/Fred Jones, Jr. (Frank Welker) - realized his father Mayor Jones was the Freak of Crystal Cove and actually took him from Brad Chiles and Judy Reeves, his real parents
- Daphne Blake (Grey Griffin)
- Velma Dinkley (Kevin Dunn)
- Sheriff Bronson Stone (Patrick Warbutton)
- Mayor Fred Jones, Sr. (Gary Cole) - revealed ???
- Barty Blake (Frank Welker)
- Nan Blake (Kath Saucie)
- Dale Dinkley (Kevin Dunn)
- Angie Dinkley (Frances Conroy)
- Colton Rogers (Michael Masse, replaces Casey Kasem to sound similar to him)
- Paula Rogers (Grey Griffin)
- Marcy Fleach/Hot Dog Water (Linda Cardellini)
- Mayor Janet Nettles (Kate Higgins) - replaces Fred Jones, Sr. after he was unmasked as the Freak of Crystal Cove
- Nova (Amy Acker) - Brad and Judy's pet dog, and Scooby's love interest
- Danny Darrow (Dwight Schultz)
- Ethan and Gary (Mitch Watson and Tony Cervone)
- Harlan Ellison (himself)
- Cassidy Williams/Angel Dynamite (Vivica Fox, Kimberly Brooks for Teenager)
- Original Mystery Incorporated:
- Professor Pericles (Udo Kier) - the Scooby-Gang's arch-nemesis, having been responsible for tormenting them such as killing their friend, Angel Dynamite, causing the injury of Nova, threatening Daphne's life and killing Marcy Fleach, he is the main antagonist of the final film seeking to free his master with the Planispheric Disk so he can be given power
- Ricky Owens/Mr. E (Lewis Black, Scott Menville for Teenager)
- Brad Chiles (Tim Matheson, Nolan North for Teenager) - Fred's biological father
- Judy Reeves (Tia Carrerre, Kari Wahlgren for Teenager) - Fred's biological mother
- Angel Dynamite (Vivica Fox) - Reason: ???
- Mayor Fred Jones, Sr. (Gary Cole) - Reason: ???
- Mr. E (Lewis Black) - Reason: ???
- Ed Machine (Richard McGonagle) - Reason: ???
- Danny Darrow (Dwight Schultz) - Reason: ???
- Professor Pericles (Udo Kier) - Reason: ???
- Brad Chiles (Tim Matheson) - Reason: ???
- Judy Reeves (Tia Carrerre) - Reason: ???
- A locket shaped like a magnifying glass found in the Crystal Cove caves and a call from Mr. E.
- Hotel sign reading "The dog dies!" and Mr. E's note claiming that Gatorsburg is "one piece of the puzzle".
- A newspaper photo revealing the kids in the locket as Brad Chiles and Judy Reeves.
- An old Crystal Cove High School yearbook
- A photo of the old Mystery Incorporated team highlighting their parrot Professor Pericles; a note from Mr. E.
- A cryptic warning from Professor Pericles; a text message from Mr. E.
- Mr E.'s associate is revealed (not to Mystery Incorporated but to the viewer) to be Ed Machine.
- Darrow Family Archives stolen from the university by Mr. E.
- A warning from an associate of Mr. E.
- A puzzle piece.
- Angel Dynamite is revealed to the viewer by Velma, but not the rest of Mystery Incorporated, to be Cassidy Williams from the original Mystery Incorporated.
- It is revealed, not to Mystery Incorporated but to the viewer, that the puzzle piece from Danny Darrow is part of a Planispheric Disk. Also revealed to the viewer is that Mr. E is Ricky Owens from the original Mystery Incorporated.
- A warning from Professor Pericles, who also reveals to Mystery Incorporated that the puzzle piece is part of the Planispheric Disk.
- Details on the purpose of the Disk and the truth behind the fate of the original Mystery Incorporated. Angel reveals her true identity to the rest of the gang. The Freak of Crystal Cove is revealed to the viewer.
- The circumstances that lead to the original Mystery Incorporated being run out of town, and Fred's real parents are revealed.
- The third piece of the Planispheric Disk.
- The fourth piece of the Planispheric Disk.
- It is revealed how Mr. E and Professor Pericles met each other.
- The ship's manifest, bearing the journals of the conquistadors who founded Crystal Cove, which describe their discovery of the treasure (a crystal sarcophagus filled with black pearls) that became the evil beneath Crystal Cove (which they named for the sarcophagus) and their use of the Planispheric Disk to mark its location after its burial; the fifth piece of the Disk.
- The repeating pattern of mystery-solving groups, including the Darrow family and both incarnations of Mystery Incorporated, being haunted by the Planispheric Disk and the treasure it leads to, all of them consisting of four sleuths and an animal mascot; the Planispheric Disk user manual.
- The lost original settlement of Crystal Cove, which vanished over three centuries ago, now submerged beneath the sea; its inhabitant missionaries were the conquistadors who were the source of Crystal Cove's curse; the base revealed to have been constructed by Frau Abigail Gluck, a member of an old mystery-solving group; her body whispers "Nibiru" upon its discovery; the final piece of the Planispheric Disk, found by Professor Pericles.
- Velma finds that the word "Nibiru" (whispered by the specter of Frau Gluck in "The Midnight Zone") refers to an ancient Babylonian prophecy of a collision between Earth and a large planetary object known as "Planet X," whose inhabitants were the first recorded instances of gods.
- Velma's primitive recorder, used on the Planispheric Disk, yields the word "Nibiru".
- It is revealed that Friar Gabriello Serra's corrupted donkey Porto sent the original Crystal Cove settlement into the ocean, not an earthquake as was originally believed. The Phantom Mummy of Friar Serra warns the gang about evoking the memory of "Nibiru". Friar Serra's statement of "Heed the warning of the alligators" is a reference to the hotel sign in Gatorsburg reading "The dog dies!" in "The Creeping Creatures".
- Velma's primitive recorder, used on the Planispheric Disk, yields the phrase "Señor P. Llave", and the coordinates to the Gatorsburg cemetery; upon reaching Señor Llave's grave, the gang find it empty, with only an old flintlock left in it.
- The gang discovers a musical phrase which has appeared on the Planispheric Disk. When the Hex Girls sing the phrase, the Disk reveals another set of coordinates, which leads the gang to the restaurant owned by Skipper Shelton, whereupon they find that his hat (given to him by Handsome Jimmy from "Night on Haunted Mountain") bears the name "S. Llave" written under the brim. Scooby visits Nova in the hospital, only to see her flatline. Just afterward, she sits up in bed and says "Nibiru. Nibiru is coming", before regaining life.
- Francilee Jackson drops her bowl as she is escorted away and the bowl is revealed to bear the words "Tercera Llave" on its underside.
- While the gang is researching the Dandy Highwayman in the town library, Scooby awakes from another nightmare and knocks the book he is reading off of the table, dislodging a piece of cloth from within the book which bears the words "Cuarto Llave" written on it. Scooby has been having nightmares since Nova's accident. In Scooby's latest nightmare, a being speaking through Nova warns him of the coming of the Anunnaki at the time of Nibiru and warns him that his life is in danger, telling him that he and his friends must destroy the cursed treasure beneath Crystal Cove. Scooby then informs his friends about his dream.
- Professor Pericles appears to be serving the Evil Entity sealed within the crystal sarcophagus, and has been on a mission to gain access to the Planispheric Disk in order to set the being free.
- The good personality components of all members of previous mystery groups and the people associated with the cursed treasure (among them ex-Mayor Fred Jones Sr., Ed Machine, Cassidy Williams, Ricky Owens, Brad Chiles and Judy Reeves) were sent to the dream dimension where they remained to stay. The very first mystery group, the Hunters of Secrets, was first manipulated by the entity within the sarcophagus; however, they were pure and realized they were being manipulated. They attempted to destroy the entity with a relic referred to as the "Heart of the Jaguar", but never succeeded due to the conquistadors' interruption. The Keys are being used by previous mystery groups (such as the Darrow Family, the Alianza Mysterio, the Fraternitas Mysterium, the Mystery Gang, and the Benevolent Lodge of Mystery) when the gang visits them in the dream world, symbolizing their use with the gates to the cursed treasure. If they destroy the entity, everyone from the dream world would be set free from the curse.
- The gang finds the Heart of the Jaguar, the spear used by the Hunters of Secrets that is able to destroy the evil entity trapped in the crystal sarcophagus. Mayor Nettles had a nightmare telling her that the gang would need her help in transporting the Heart of the Jaguar back to Crystal Cove.
- The passageway to the cursed treasure is found and opened. Professor Pericles confirms Cassidy's death to a troubled Mr. E, who is worried about her and is saying she was right the entire time. Velma's computer model of the Planispheric Disc perfectly mirrors the planets in the solar system. The planets are coming into direct alignment and the tenth planet, Planet X, is getting closer and is about to come into alignment behind Pluto and will cause a massive gravitational disruption, one not seen in 5,000 years. The time of Nibiru happens in two days. The gravitational disruption makes the fabric between dimensions of time and space weak, which is why the evil entity buried beneath Crystal Cove must be destroyed. Along with destroying the entity, the Heart of the Jaguar will undo all of its evil.
- The Evil Entity which was sealed in the crystal sarcophagus is released from its imprisonment. It tells the gang that it brought them together as it brought together those groups before them, solely for the purpose of releasing it; the gang realizes that everything the Entity is saying is untrue.
- The overall mystery is solved. By destroying the Evil Entity, the gang created an entirely different timeline. No one has been negatively influenced by the Evil Entity. Everything has come undone; the gang's actions have created a perfect world where they live productive and normal lives. Harlan Ellison, who is now called Mr. E, contacts the gang and tells them he knows who they are. He knows that they created an alternate timeline called, the Hanna Barbara Cinematic Universe, by destroying the Evil Entity, due to him being a genius and his hypertuned psychic and hypnotic connections with alternate dimensions, which is why he is able to remember every timeline ever created. However, he mentions that the gang has slipped the timestream with him. He has admitted the gang (including Scooby) to be in his class next semester and he mentions there is a lot of meddling to do and a lot of mysteries to be solved.
- Evil Entity (Clancy Brown) - the true main antagonist and the Greater Scope Villain of the whole Scooby-Doo series having been responsible for people dressed like monsters and others such as Pericles, his goal is to be free from his prison so he can gain a host