The shadow people
Shadow people have been reported for as long as humans have been on the planet. In folklore shades are though to be spirits of the dead. More recently videos have appeared purporting to show shadow people or entities.
In mythology, Shades are known as the spirits or ghosts of the dead who reside in the underworld. This is often equated with Hell. In Hebrew, a shade was known as the Death Shadow. Moreover, the underworld was one of three other worlds, apart from our own, that were part of Shamanism. These being the upper, middle, and lower worlds.
Recently video evidence of "shadow people" has been uploaded to various video-sharing sites. Of course, these should be cautiously approached, as many may be fake or CGI. However, shadow entities have been observed on live streams that cannot be faked. Therefore, here they are analyzed with an open mind. Moreover, this kind of phenomenon has been reported for many centuries. long before YouTube!
Speeded up manifestations
Often the black shape seen in videos seems to be moving too fast. Of course, this could just be bad CGI. On the other hand, could the entities be from a dimension where time is running at a different speed? In fiction, time in the Narnia series, by C.S Lewis, passes at an accelerated rate, a year on Earth was 52 years in Narnia:
"The series tracks the story of Narnia when humans, usually children, enter the Narnian world from Earth. The entire Narnian timeline, from its creation to its end (c. 1–2555), ran parallel to 49 Earth-years (c. 1900–1949), thus on average a year on Earth meant 52.14 time dilation years in Narnia." Wikipedia.
A black mass
Manifestations caught on video range from an amorphous black mass to a more defined human shape. The above still is from a video by slapped Ham. It shows a black mass encroaching into a room. One of the more defined manifestations is shown below.
Sometimes shadow entities are more defined and show facial features. However, pareidolia may also be a factor in these images.
The author postulates that the most likely explanation for shadow people is that they are spirits of the dead. They have not passed over and are stuck on Earth in a timeless state. One other possibility is that they are agents sent into our universe to drive people away from a particular location. These locations could provide a weak point between different dimensions of space and time. Consequently, they are used as entry points. This has been suggested in fiction, such as in Alan Garner's Elidor:
"Nicholas and David are lured into a ruined church, where the fabric of time and place is weak enough to allow them into the twilight world of Elidor"
If we are living in a simulated universe shadow entities could be agents from outside the program sent in to change the outcome of the timeline in some way. They could also be avatars that are somehow corrupted and erratic.