Leviathan

The Leviathan is a giant Atlantean artifact that was left near the underwater entrance to Atlantis so that it could protect the city from intruders. Being longer than a submarine, the Leviathan is a mechanical monstrosity that closely resembles a lobster. It is a Character of the Dream World.

Background
Nearly 8,000 years later, The Leviathan spots Marina (Mermaid) and Flounder swimming about in it's Territory. He immediately attacks Flounder and begins a chase going through the Tunnel to the Entrance to Atlantis. Unfortunately, Marina manages to outwit the Creature and the Leviathan sleeps while guarding Atlantis.