Scooby-Doo! and the Goblin King (2008)

"To face a goblin king, courage is crucial. So for Scoob and Shaggy, the odds are against them!"

Scooby-Doo and Shaggy must go into the underworld ruled by The Goblin King in order to stop a mortal named The Amazing Krudsky who wants power and is a threat to their pals: Fred, Velma, and Daphne.