In this third and final installment of the live-action franchise, Scooby-Doo and his friends go for a reunion at Crystal Cove, when suddenly a ray transports them to an alternate dimension where they encounter their teenage young selves, as they must work together to fight the villain dubbed, "Lady Manta".
March 25, 2011
- Mystery Inc. (2002):
- Scooby-Doo (Neil Fanning)
- Shaggy Rogers (Matthew Lillard)
- Fred Jones (Freddie Prinze, Jr.)
- Daphne Blake (Sarah Michelle Gellar)
- Velma Dinkley (Linda Cardellini)
- Mystery Inc. (2009):
- Scooby-Doo (Frank Welker)
- Shaggy Rogers (Nick Palatas)
- Fred Jones (Robbie Amell)
- Daphne Blake (Kate Melton)
- Velma Dinkley (Hayley Kiyoko)
- Lady Manta (Vanessa Marshall) - the main antagonist and the one who has the ability to travel through parallel dimensions, her appearance is masked woman whom based off a manta ray, her goal is to claim the Scooby Doo legacy.
- Leslie Wilkins (Alfonso Ribeiro) - the gang's old classmate in Crystal Cove University
- Principal Aaron McCoy (Colm Feore) - the gang's principal at Crystal Cove University
- ???/??? (???) - the culprit of the 1969 moon mission on the moon disguised as ???, Reason: ???
- ???/Skeleton Caesar (???) - the culprit of the Ancient Greece mystery disguised as Skeleton Caesar, Reason: ???
- ???/??? (???) - the culprit of the Jurassic Park with dinosaurs, with ??? disguised as the ???, Reason: ???
- Captain Cornelius Cutler/Ghost of Captain Cutler (Jemain Clement) - the culprit of the Scuba Diving Mystery with pirating treasure disguised as his own ghost, Reason: to pillage the ships.
- ???/??? (???) - the culprit of the Mystery of when the gang were shrunken down to miniature size chasing down the person controlling the bugs to ???, Reason: ???
- ???/Shogun Samurai (???) - the culprit of the China Dojo Mystery disguised as the Shogun Samurai, Reason: ???
- ???/Mummy (???) - the culprit of the Sphinx mystery disguised as the mummy, Reason: ???
- ???/Black Knight riding Dragon (???) - the culprit of the Dragon mystery, with ??? disguised as the Black Knight, Reason: ???
- Amanda Troy/Snow Ghost (Vanessa Marshall) - the culprit of the Antarctica mystery with a oil escavation disguised as Snow Ghost, Reason: to claim the deed to the oil rig, later revealed to be Lady Manta, whom exposed Lord Manta's plans.
- James Smithers/Lord Manta/Leslie Wilkins (Guy Pearce) - son of Old Man Smithers, the gang's arch-nemesis who caused Mystery Inc. to disband in the first place, Reason: to ruin the reputation of the gang, and claim the glory.