Scooby-Doo 2 : Monsters Unleased is the sequel to the movie Scooby-Doo , released in 2004 by Warner Bros. Scooby-Doo 2 : Monsters Unleashed is a 2004 film , and sequel to 2002 's Scooby-Doo based on the Hanna-Barbera series classic , Scooby-Doo .