The are called croists. They are sea monsters living deep within this mysterious ocean. They hunt prey for unknown reasons but they don’t eat it. They are so rare that they were not even seen by humans even once (maybe because there’s only two) they may be almost as smart as humans and might even have some similiar behavior in some things (like poses or so). The males have these weird tails to swim in better speeds and to attract mates while females have horns on their head, whoever is unlucky enough to get empaled by the horn will get mind controled (or however you spell it) to doing whatever she likes.