- For the remake SyFy series' version of demons, see Demon (Syfy)
Earth and the Other Side
Demons are a mysterious and malevolent supernatural species related to the Other Side. The Men with Sticks and Rope and possibly the Devil are types of demon. Demons can have children with humans, spawning succubi/incubi.
Demons are a mysterious paranormal species whom very little is known about overall. Many different types of demons with variations between them apparently exist. Some demons such as Yvonne Bradshaw's father are capable of living on Earth for a time and even of having children with mortals, while other demonic entities such as the Men with Sticks and Rope cannot leave the Other Side for long and thus usually only project themselves on Earth through doors and electronic equipment. One common characteristic between demons seems to be that all of them have very malicious and sadistic tendencies by nature: the gatekeepers of the Other Side are known to be very brutal and sometimes even sadistic with ghosts, the Devil exists to create chaos and spread apocalyptic corruption, and the demon who conceived Yvonne was apparently "beautiful and cruel."
Though unconfirmed, Dominic Rook piled together in his emails several characteristics that he believed demons (at least ones capable of existing on Earth) have. He believed that demons existing on Earth can probably shapeshift, taking on human or animal form at will; and that they have similar abilities to ghosts, including invisibility, superhuman strength and mindreading.
The Men with Sticks and Rope are demons who serve as the gatekeepers of the Other Side. They mercilessly hunt ghosts who have not crossed over despite lack of unfinished business, and they also interact with newly-recruited vampires during the period of temporary death before their transformation is complete. They apparently to some extent report to the Devil as his minions. The Men with Sticks and Rope can briefly project themselves into the world of the living through electronic devices or through control over the doors, but they usually cannot fully cross into the mortal world, and they can't survive on the earthly plane cut off from their world.
Incubi (male) and succubi (female) are supernatural creatures born of a union between a human and a demon. They have the ability to cause anyone of the opposite gender that they touch to become irresistibly attracted to them for as long as they're near the incubus/succubus, and anyone who has sex with an incubus/succubus dies (unless they are an undead creature like a vampire). (Hold The Front Page)
Though never actually confirmed, it is thought that the Devil is a demon. He was created by God to act as a force of chaos. The Devil is an incorporeal entity which must possesses a human vessel when on Earth, and he has a wide range of very powerful supernatural abilities even when he's weakened. The Devil has a parasitic relationship with vampires and werewolves, feeding on the conflict between them, and when he's at full power while in physical form, he is capable of wreaking the Apocalypse upon the world. The Devil can only be weakened and rendered killable through trinity magic. (Series 5)
Yvonne Bradshaw's fatherEdit
Yvonne's father was a demon who conceived Yvonne with a human mother. Very little is known about him. Unlike the Men with Sticks and Rope, Yvonne's father was capable of manifesting and living on Earth, and of conceiving a halfbreed child. Yvonne stated that her mother had described her demonic father as "beautiful and cruel." (Hold The Front Page)
Men with Black, Black Feathers on their Black, Black WingsEdit
"Men with black, black feathers on their black, black wings" were mentioned by the gatekeepers of the Other Side to Annie when they were trying to force Saul to take her into Purgatory. These Men with Black, Black Feathers on their Black, Black Wings were implied to inhabit Purgatory and to work with the Men with Sticks and Rope. It was also implied that they're involved in punishing ghosts who hadn't crossed over when they're taken to the Other Side by force.
- Demons are apparently so mysterious that even the Department of Domestic Defence hardly knows anything about them and hasn't even classified them.