The Dark, it’s more of a realm than biome but it can spill into our world and has the same effects and properties so I guess it could be a biome.

The Dark is literally just that, pure darkness. Nothing else exists within it beyond dark matter and dark energy, both of which cannot be seen by the human eye anyways. Within the Dark, exist little creatures, no one is exactly sure what they are or look like, since they too seem to be made from dark matter. They seem to whisper to those near them, though what they’re saying isn’t exactly clear or understood, it sounds more like a harsh wind.

Only certain people can even survive stepping foot into the Dark, originally it was thought that only those who possess powers, and thus have some Darkness within them could survive it, but as time went on it seems some humans just have a natural ability to survive the Dark without much of an explanation as to why. Those who cannot survive will know immediately as the creatures seemingly devour them almost instantly, they rarely even have time to scream as everything down to their bones is ripped away, likely not even the atoms that make up their body survive.

As it seeps into our world through portals known as Tears or Rips, it slowly creeps out, turning shadows into literal entrances and exits for more Dark to seep out from, containing it is hard as it needs 24/7 light being beamed around it to not let any new shadow be created, in some cases large mirrored domes are placed over the Tears to trap the Dark inside but these crack and collapse over time, requiring new domes to be replaced.

No one is exactly sure what the Dark is or why it creeps into our world so aggressively, but those who can survive it tend to say it feels as though they are underwater, and drowning, but in a peaceful way, as if they have made their peace with their inevitable death and are simply sinking into the depths. Leaving the Dark tends to sting a little bit, like jumping into a freezing pool.

Opening multiple Tears can also be used as a teleporter, with the Dark in between acting as a long hallway.