This is an infinite expanse that exists as the space between Cosms, as well as between universes. The Twisting Nether is a realm of pure energy with physical areas inhabited by those creatures hardy enough to survive the harsh conditions. It is the home of demons and the Burning Legion.
The Twisting Nether is the source of magic and is also suffused into the fabric of each universe, leaking through to allow sentient beings to access magical energies. Each universe has its own Twisting Nether, with its own version of the Burning Legion.