He-Man and the Masters of the Universe S01 E06 The Deep End

"A sword will choose a master, a boy will become a man, and a hero will be born."

An unexpected power surge across Eternia prompts the heroes and villains to search the Sea of Rakash for answers. It becomes apparent that the Coridite crystal, long though destroyed, still exists in the possession of Mer-Man. Man-At-Arms manages to grab the Coridite but Mer-Man prevents the hero from escaping. Just as Mer-Man is about to retrieve the crystal, his large fish ally swallows Man-At-Arms and the Coridite crystal! Unexpectedly, the Coridite causes a mutation inside the giant fish, making the creature extremely powerful and dangerous...