Zombie Island was produced by Hanna-Barbera (just two years before its absorption into Warner Bros. Animation). The script by Glenn Leopold (a veteran of Scooby-Doo and The Real Adventures of Jonny Quest ) and Davis Doi was deliberately written to subvert expectations. The directors, Jim Stenstrum and Hiroshi Aoyama, pushed for a darker, more cinematic look.
This is the film’s most famous departure. The zombies are real, the villains are immortal werecats, and the stakes are death (or eternal soul trapping). The film has genuine jump scares, atmospheric dread, and a body count (implied past victims). Scooby-Doo on Zombie Island