Hood Episode Four
The Ancient spirit who welcomes the Hunter to the Spirit World tells him about the demon who controls Cameron. Long, long ago, this demon killed the Ancient spirit and his companions. It is a very powerful entity, capable of dominating people's minds from the Spirit World and possessing them without a contract. No other known demons can do such things; they are bound by the laws of their existence. Somehow the Archdemon is not. It likes to manipulate people by making them believe it is a loved one, drawing them to it, and then using their bodies in reality. This is what it did to Cameron, making her think she was communicating with her beloved grandmother.
The Archdemon controls a section of the Spirit World. In this place where it hides, the debris of lost and forgotten memories gathers. The demon conceals his presence behind these walls and uses wards in an effort to trick and confuse the Hunter.
The Archdemon is inside a copper box made by the Dead Race. The way into the box can only be opened by the "song of a white jay as heard by Them". Inside the copper box, the Archdemon rests, but this box is actually the prison of the fiends, terrible demons one thousand strong that were imprisoned by the Dead Race eons ago.
The Archdemon stands before Cameron when the Hunter opens the door. It has a hulking form, a wild, animated mane, and many eyes, which are asymetrically placed around its face. A long horn juts down from either side of its head, which is crowned with sharp antlers. Two ridges run down its forehead; they end in openings that are possibly nostrils. A gaping mouth filled with spiked teeth sits under an unually-folded lip. The Archdemon looks intelligent.
The Hunter attacks with his blade, but Cameron parries with a sword of her own, still convinced this demon is her grandmother. The Hunter knocks her out. The Archdemon says it has killed three hunters before him, but it is no match for the Fenrirr who now stands before it.
Kingdom Of Liars
In Kingdom of Liars episode 3 in becomes clear a Blackheat Spirit used the Archdemon as bait. The Archdemon had to be sacrificed so the thousand fiends could escape.