Scary ocean mobs/boss

I want something to be scary when I go into the ocean. Similar to the warden but you could find it in ocean ravines. Something that you don’t want to run into. It would give the ocean an eerie vibe and you would have to prepare before going there. It could possibly have a light to help it see. When you kill it it would drop a light you can use in caves. You could hold it in your hand or in your offhand and it would light everything up around you. Thanks for reading