Shadow person

A shadow person (also known as a shadow figure, shadow being or black mass) is the perception of a patch of shadow as a living, humanoid figure, and interpreted as the presence of a spirit or other entity by believers in the paranormal or supernatural.
History and folklore.
A number of religions, legends, and belief systems describe shadowy spiritual beings or supernatural entities such as shades of the underworld, and various shadowy creatures have long been a staple of folklore and ghost stories, such as the islamic Jinn and the Choctaw Nalusa Chito.
The "Coast to Coast AM" late night radio talk show helped popularize modern beliefs in shadow people. The first time the topic of shadow people was discussed at length on the show was April 12, 2001 when host Art Bell interviewed Native American elder Thunder Strikes, who is also known as Harley "SwiftDeer" Reagan. During the show, listeners were encouraged to submit drawings of shadow people that they had seen and a large number of these drawings were immediately shared publicly on the website. 
In October that year, Heidi Hollis published her first book on the topic of shadow people, and later became a regular guest on "Coast to Coast". Hollis describes shadow people as dark silhouettes with human shapes and profiles that flicker in and out of peripheral vision, and claims that people have reported the figures attempting to "jump on their chest and choke them". She believes the figures to be negative, alien beings that can be repelled by various means, including invoking "the Name of Jesus".
Although participants in online discussion forums devoted to paranormal and supernatural topics describe them as menacing, other believers and paranormal authors do not agree whether shadow people are either evil, helpful, or neutral, and some even speculate that shadow people may be the extra-dimensional inhabitants of another universe. Some paranormal investigators and authors such as Chad Stambaugh claim to have recorded images of shadow people on video.
Shadow people feature in two episodes of ITV paranormal documentary series "Extreme Ghost Stories", where the phenomenon is described as a "black mass".
Scientific explanations.
Several physiological and psychological conditions can account for reported experiences of shadowy shapes seeming alive. A sleep paralysis sufferer may perceive a "shadowy or indistinct shape" approaching them when they lie awake paralyzed and become increasingly alarmed.
A person experiencing heightened emotion, such as while walking alone on a dark night, may incorrectly perceive a patch of shadow as an attacker.
Many methamphetamine addicts report the appearance of "shadow people" after prolonged periods of sleep deprivation. Psychiatrist Jack Potts suggests that methamphetamine usage adds a "conspiratorial component" to the sleep deprivation hallucinations. One interviewed subject said that "You don't see shadow dogs or shadow birds or shadow cars. You see shadow people. Standing in doorways, walking behind you, coming at you on the sidewalk." These hallucinations have been directly compared to the paranormal entities described in folklore.
Finally, visual hallucinations, such as those caused by schizophrenia and bipolar disorder, may appear to be shadowy figures at the edge of peripheral vision. 
In popular culture.
The 2014 https://en.m.wikipedia.org/wiki/The_Babadook 
Is about a dark shadowy figure that start messing with a boy with behavioural difficulties and his single mum trying to cope on her own with neither getting much sleep. It's start with a pop-up-book they find in the bookcase. The writer direct says it's based on true occurrence of a personal friend. Also many people who are haunted by shadow people refuse to watch much of the film due to the likeness of "The Babadock" to their own experiences. 