sunken depths

The sunken depths could be something akin to the deep dark in the fact that its like a new zone in minecraft. perhaps one based on a new mechanic or thing the player has to do, like for example, perhaps the sunken depths is home to some tentacle monster, and the tentacles are chasing the player or rather if the player isn't careful and is just swimming out in the open, they could get caught by these massive tentacles and thus get damaged a lot. perhaps, there could even be mechanic or new blocks that even make things harder to breath or pose a new danger, even with water breathing potions or other such things. also, could/would work as a biome, so wouldn't be exactly like the deep dark where just going deeper in the ocean leads to this biome and thats what this would lead to. the biome could appear more rarely but, would be an interesting find and place to venture through.