Realm of Phantoms
Tenamus is a forlorn Realm whose last whispers of hope were butchered eons ago. When this world fell to darkness, its denizens did not go quietly into the cold night. They raged against the darkness and clung to the final moments of Tenamus' violent death throes. While the undying Phantom-Kings used paraystic magics and machivellian deals to bolster and sustain the magic that now held their broken world together. A corruption that has mutated all life on Tenamus and created a world of true malicious evil in the Cosmos.
Imagine an endless landscape made of black stones, dry earth, and dying plants. Now imagine above it is a great storm of darkness that is slowly consuming all light. As you walk across it, the ground begins to crumble and shatter revealing that the realm is actually hollow, but not empty. Inside it are the nightmares of the cosmos. You look down into the darkness and the darkness returns your gaze.
There is an actual magic black hole above the realm draining it of power, slowly crumbling it away.
Phantoms, Undead monstrosities that use Souls as a fuel source for their magic. They have made deals with dozens of realms and been the death knell to hundreds more. Inside the realm are entities older than time itself, they are beyond sophonce. They may be elemental.
Much of it has died off from life being drained, what does remain is able to survive off corpses, darkness, and evil.
Nightmares, great steeds made of shadows and hate are an example of the few reamining fauna to Tenamus. Each beast that remains is a mockery of the once verdant realm Tenamus was once in a history long past.
Energy, even Faith and Glow, is hard to acquire on this realm. It is all sucked up into the great black hole.
There are no scientific advances anymore, only new ways to wield corrupting magics of shadow and decay. The beings trapped on this realm know of the future, the past, and the present. They use fear as a source of magic rather than anything else used by everyone else in the cosmos.