Demons are created when a vampire and a born werewolf have a child together, making them incredibly rare.

Chaos

Demons have chaos-inducing abilities but only in small amounts, like moving objects and changing the tempurature in an area or of a person. The amount they can affect is expanded if they get more power, which is gained over time as they age, so an older demon is much more powerful than a younger one; they also gain temporary power if the summoning spell thing is completed. The power gained from that spell lasts until they are removed from this plane of existence and sent back to hell.

The summoning spell thing is when a demon is summoned. It starts with a witch summoning them by killing five different supernatural types. The demon then has to kill the same five different types, in reverse order. Therefore, if the witch killed a werewolf, vampire, siren, human, and then a witch, that means the demon would have to go witch, human, siren, vampire, werewolf.

Demons can only be "killed" through the following means: A powerful witch doing a spell to send the demon back to "hell" until they can get back out; The demon in question failing the summoning spell, such as by killing supernatural being sin the wrong order; Or by the demon in question being pulled back from the inside. There is no way to completely destroy a demon permanently.