Submitted by Anonymous
Scooby-Doo and Shaggy become best friends as kids before meeting Fred, Daphne, and Velma, and devoting their lives to solving mysteries. The fiendish Dick Dastardly wants to use Scooby and the three skulls of the ancient dog Cerberus to open the gates to the underworld to free his old friend Muttley and steal the treasures within. Scooby and Shaggy team up with their hero, the Blue Falcon (actually his son Brian) plus Dynomutt and Dee Dee Skyes to stop Dastardly.
Dastardly kidnaps Fred, Daphne, and Velma, who learn of his true plans. After he gets all the skulls, Dastardly opens the portal and unleashes Cerberus. He and Muttley go after the treasures, while the heroes send Cerberus back inside, but the prophecy states that a man and dog who are best friends must close the portal with one of them staying behind. Shaggy chooses to stay behind, but they soon find an inscription that Scooby reads to bring Shaggy home. Dastardly and Muttley are then taken into custody by Brian and his team.
The gang expands their Mystery Inc business and continue to solve mysteries.