Lesser spirits

Not to be confused with the Demon.
"(...) These forces have many uses beyond those of the covetous demons and have appeared around the world where the fabric between the living and the damned is thin." The Night Shift Database
The Lesser Spirits are entities employed by the Demon to haunt, startle and attack the player during the night shifts in the Mortuary Assistant.
According to the Lesser Spirits entry in the Night Shift Database, the Demon's powers are limited, forcing them to use the Lesser Spirits as tools to reach within the world of the living.
While the Night Shift Database mentions there being various entities, there are only three Lesser Spirits that manifest during the game, disrupting the player.