Deep Sea biome and new mobs

A new biome in the oceans that reaches to negative y levels. It would have a light level of 0. Could introduce new passive mobs such as anglerfish, jellyfish and siphonophores which emit a light level of 1, as well as a new large hostile mob called the leviathan. Shipwrecks could be more common here, as well as a new structure. Could also include a new ore (aquasite) which makes tools and armour on same level as netherite but is very rare.