The Nightwalker is a void-undead, an absolutely black humanoid without features. It is a creature of the Negative Plane: pure negative energy condensed into a humanoid form, a direct emanation of the entropy that governs the outer planes of non-being. It has no traits and no face, the negation of all form.
Orcus, demon lord of the undead, has dominion over such emanations. The creature operates in the context of Los Condenados.