New sea hostile mob

Ocean biomes and mobs- except the nautilus - are very old and being real everyone is used to it. Drowneds are the only threat within these biomes excluding guardians and their elder counterpart and they are exclusive to a structure. A new mob such as an eel in similar scaling to the spider would fit greatly with any biome and add that little extra challenge that the ocean really needs. Could also have an electric version which can temporarily stun the player for 3 seconds or so.