The Pirates of Dark Water - S203 - The Beast And The Bell

Ren sees a vision of his father telling him if he rings "The Bell of the First Sound" that all the Dark Water will be gone forever. But when he rings the bell, he finds out that it was all a trick by an imprisoned servant of the evil Dark Dweller, a creature named Keroptus. Ren swears to re-imprison the monster he freed by accident.