A nightwalker was a type of nightshade; a sentient undead monster from the Plane of Shadow. It was unnatural and malicious, and it took delight in the corruption and suffering of others. It was a creature of both death and shadows, and had enormous powers over darkness.
A nightwalker's body looked as if it was made of shadow-stuff, with a vaguely humanoid form. They were about the size of a house, but were usually no taller than 20 ft. (6.1 m), and their bodies were smooth and hairless.
Nightwalkers were the shades of extremely strong-willed and evil mortals whose ancient and unyielding will and malice allowed them to hold their corporeal shape.