Shadowfel

The Shadowfel is a plane very close to ours in the multiverse, it's a mirror plane of the prime material (places correspond roughly 1 for 1, travel 10 miles in one plane and you will travel about 10 miles in the other), and has the aspects of darkness and death. The Shadowfel is continually dark, the midday sun shines only as brightly as a full moon we are used to, and races without enhanced vision will have difficulty operating normally. Most of the plane that has been explored by Athesians consists of a vast grey wasteland with dead and gnarled trees forming small sparse forests that dot the landscape, the one notable exception being the city of Ombria, the seat of the Dark Emperor's power. Access to the plane is controlled by the Shadow Weavers, who maintain a small toehold and guard the only known fixed portal.
Think like Bloodborne or Dark Souls aesthetic.
==Notable NPCs==
The Dark Emperor
The ruler of the city of Ombria, and possibly the entire plane of the Shadowfel, the Dark Emperor is an extremely powerful being. He was once fought by the heroes of Athesia, who proved to be too much effort to conquer. The Dark Emperor is capable of changing his appearance and has been seen as a dark glowy ball of energy (sort of inverse will-o-wisp), and as a colossal armoured titan (like Sauron).