The Divers Dread, Dunkleosteus

Since the over world doesn't have a proper boss, I think you should add one. Dunkleosteus would be a boney fish a little bigger than the ravenger, it only has one attack which is a bite attack and it has a small cool down. Dunkleosteus would only spawn in shipwrecks and have a small chance of spawning at all, but its a big enough chance that you would find it at least once if you explore the ocean. If you kill it, it drops bone blocks or bone and it has a 50% chance of dropping an enchanted trident. The Dunkleosteus is meant to add a sense of fear to the ocean, since its kind of hard to get your stuff back after you've died under water