Demons

The Demons are Monsters kept inside the Facility. They are listed on the Whiteboard, but are not bet on, nor are they seen at anytime during the System Purge.

Physical Descriptions and Attributes
The appearances, characteristics, and number of Demons is unknown, as they are not seen in their Cube Prisons or Purge. It is quite possible that no scenes with the demon were ever filmed, and that they were named on the whiteboard simply in order to represent a common horror movie category. Alternatively, any otherwise unnamed creature seen in the facility could theoretically be a member of the demon category. However, the universal appearance of Demons can most likely be attributed to them; humanoid creatures (male or female), with devilish features such as strangely tinted skin, long, sharp finger and toe nails, horns on the tops of their bald heads, pointed teeth, sunken or glowing eyes, and sometimes wings. The Demons might also take on a more ghostly or supernatural appearance, similar to how the Wraiths might look, and use dark magic and demonic possession as their weapons.

In the The Cabin's Cellar, it is unknown what object directly summons them, but its possible that a Ouija board or some sort of demonic, dark magic scripture or occult book such as the Satanic Bible could summon them.

Inspiration
Demons are one of the oldest known antagonists in Ancient Mesopotamian religion, Christianity, Judaism, Islam, Hinduism, Celtic mythology, literature, European folklore, and modern media. They have their origins in the ancient legends of Persia and the stories of Ormazd, the god of creation, who fought Ahriman, the god of evil and prototype of the Biblical Devil. Later cultures such as the Babylonians and Hittites later adopted characteristics of ancient demons to apply to evil gods, such as Baal. In the horror genre, demons typically have some kind of physical presence. However, in other works demons possess no physical body at all and are completely incorporeal and invisible, manifesting themselves entirely through possession of other beings.

In literature and movies, demons are usually represented in one of three forms. One is that of very ancient beings forgotten on Earth, such as the those in the Chthulu Mythos. The second type are evil gods from ancient mythology, such as Baal or Pazuzu, and are usually assisted by hordes of lesser demons or goblins. The third type are the evil spirits of human beings who continue to exist by feasting on the souls of the living, such as Freddy Krueger from the Nightmare on Elm Street franchise.

Some examples in TV, film, and literature include:
 * Demons by Lamberto Bava, in which they are fast and vicious with long nails and long splayed teeth for tearing flesh.
 * Night of the Demon
 * "Sometimes They Come Back" (Short story)
 * Sometimes They Come Back (Film)
 * The Exorcist (novel)
 * The Exorcist (film)
 * Hellboy (2004 film)
 * Hellboy II: The Golden Army
 * Hellboy: Sword of Storms
 * Hellboy: Blood and Iron
 * Hellboy: The Science of Evil
 * Hellboy: The Black Wedding
 * Hellboy: Pyramid of Death
 * Hellboy: The Yearning
 * Hellboy: House of the Living Dead
 * Hellboy: The Chained Coffin and Others
 * Hellboy: The Right Hand of Doom
 * Hellboy: The Troll Witch and Others
 * Hellboy in Hell
 * Fantasia (1940 film)
 * This Is the End
 * I, Frankenstein
 * Season of the Witch (2011 film)
 * Doom 3
 * Night of the Demons
 * Supernatural
 * The demons seen in Charmed or in Buffy the Vampire Slayer.
 * Demons appear during an occult ritual in the 2016 Irish horror film A Dark Song, where they resemble decaying human beings.
 * An invisible, immaterial and almost unkillable demon is the primary antagonist in the Denzel Washington film Fallen.