These monsters, like the Beings of Xiclotl and the Death Vines, are obscure creatures not well known even among the most learned scholars. These beings are described as two-dimensional beings of shadow that can only move in horizontal movement and are known to hunt humans with cruel delight until slaying them outright. Other accounts describe them as a type of shadow elemental of the malicious variety that can teleport into different realms and can shoot out shadow-like tendrils that suck the engulfed victim's body fluids, leaving nothing but a dried up corpse once its done.
Behind the Mythos
The Adumbrali were created by Robert A. W. Lowndes and expanded by Chaosium.