Shadow Beings are mysterious entities believed to be of extradimensional origin.
Overview
They are mysterious smoke like entities comprised of unknown matter. In their true appearance, they resemble black shadowy clouds however they can change shape at will, even being able to assume a humanoid form as well as others. These entities are widely believed to be responsible for the shadow people phenomena in which people claimed to have seen a moving shadow, usually with a humanoid shape, either out the corner of their eye or in direct sight.
Humans aren't the only species to have witnessed them as a few other worlds claim to have had sightings of similar beings which could imply that they are a universal phenomenon.
Behaviour
Their behaviour is very mysterious as they only seem to lurk in dark areas and observe individuals, usually out of direct sight. However there are a few rare cases in which a shadow person has actively attacked an individual or scared them.
The reasoning for this behaviour is not yet understood.
Theories
It is widely believed that they originated from another universe that differs from our own which would explain their abnormal physiology, however, how they travel from their reality to ours is not known although dimensional rifts/portals are a possibility.