Dark Abyss Void

A biome which you can accidentally find yourself in on the first run mid game, where entering from very deep down youd find yourself into a tectonic plate crack which is hard to tell at first, going into you find yourself in a very dark biome with what looks like tendrils all over the surface, trying to grab at the player(s). Going down here has no story reason, in fact it’s really dangerous, but at the end there’s bioluminescent algae and types of jellyfish creatures that would live down there in their own little safe haven. If you manage to survive down here you could be rewarded with a rare jellyfish creature egg, and that could be this games version of the cuddle fish(or an added new one if there’s already something like that)

Good idea, but the jellyfish actually scary, it would be soo cool if you dive into the unknown and only after 200 m into the biome you realise that you were swimming in jellyfish infested waters, (because they are so translucent). Then you really panic wich is fun.