When I think of the countless hours I spent watching Scooby-Doo as a child, I wonder whether my time couldn’t have been spent on something less damaging to my brain, like eating lead paint. But at least I’m qualified to report that this piece of junk faithfully re-creates the Hanna-Barbera formula of scary monsters, flimsy mystery, and watery comedy. Freddie Prinze Jr., Sarah Michelle Gellar, Linda Cardellini, and Matthew Lillard are the quartet of oddball detectives who drive around in a psychedelic van, accompanied by their wacky, computer-generated Great Dane. Raja Gosnell directed; with Seth Green, Alicia Silverstone, Peter Boyle, and Tim Blake Nelson. PG, 93 min.