I have no idea what could have possessed a writer to come up with this intoxicating mixture of Scooby-Doo and Hollywood parody. Well... I guess it was the 70s!... The idea is that Scooby quits his Saturday morning show in pursuit of more challenging roles and box office success helped by Shaggy, his trusty side-kick. This was inspired by those awful cartoons in the 40s in which Bugs Bunny and Elmer Fudd act like real actors even talking to Mr. Warner - their boss!!! In the same awfully unfunny way, Shaggy and Scooby barge into the Studio Director's office in order to show him samples of their work which parodies westerns and stupid 70s musicals (like Saturday Night Fever).
In the end of all this Scooby(after messing up everything he tried to do) is convinced by hordes of children chanting "Scooby-Doo, we need you!" to go back to his regular show.
After watching this very stupid attempt at a longer animated Scooby-Doo film, the viewer is convinced the awfull jokes in the Scooby-Doo show aren't really that bad and is actually looking forward to a line like "If it hadn't been for you pesky kids..."