Abyth

The Negative Plane is a place of death, anathema to all living things. Yet there are some who would tap into its fell power and use its energy for sinister ends. Most individuals prove unequal to the task. Those not destroyed outright are sometimes drawn inside the plane and replaced by nightwalkers—terrifying Undead creatures that devour all life they encounter.

One can reach the Negative Plane from the Shadowfell in places where the barrier between the planes is thin. Stepping onto the Negative Plane is almost always fatal since the plane sucks the life and soul from creatures, annihilating most at once. The few who survive by sheer luck or by harnessing some rare form of protective magic soon discover that they can’t leave as easily as they arrived.

Worse, for each creature that enters the plane, a nightwalker is released to take its place. In order for a trapped creature to escape, the released nightwalker must be lured back to the Negative Plane by offerings of life for it to devour. If the nightwalker is destroyed, the trapped creature has no hope of escape.

Generally, a nightwalker on the Material Plane is attracted to elements of the world associated with the creature responsible for its creation, which can provide clues as to who the trapped creature is. This attraction doesn’t indicate a willingness to engage with the world, though; nightwalkers exist to make life extinct, and they prioritize anything associated with the trapped creature for destruction.