Adumbrali

The Adumbrali, a.k.a. Shadow-things or Living Shadows, are a mysterious species of sadistic, extradimensional entities. The Song of Yste describes them as "beings of incredible power and malignancy, which dwell without the veils of space and time such as we know it".

Biology
The Adumbrali are dark amorphous creatures with numerous thread-like tentacles that can be expanded or contracted at will. Their bodies are two-dimensional, appearing as mere shadows. Although they are capable of changing their dimensional plane to interact with tridimensional beings, they can only do so blindly, by trial and error.

The Adumbrali also have the mysterious ability to create "seekers": life forms that mimic the appearance of beings native to other realms and planets to interact with them. These "seekers" are able to hypnotize other species and transport them to the realm of the Adumbrali.

Victims of the Adumbrali, once returned to their own worlds, are found in a death-like state, completely bloodless although with not a single wound or perforation, with eyes that can't be closed, and inexplicable glowing marks over their bodies which change shape mysteriously.

Appearances

 * "The Abyss", by Robert A. W. Lowndes (1941)