Demons

A Demon is a vile, corrupted being that's origins lie in the Disordering. They are creatures motivated purely by malice, and enjoy the destruction and perversion of any living being. Killing a Demon is commonly regarded as impossible, due to their ability to reform again after their defeat.

Posession
Since Demons are very often easily identified, and since there are overwhelming hatred and fear of them, most prefer to spend their time possessing a being. They usually also enjoy the torment that possession inflicts upon it's victims, however the act of possessing and maintaining control on a body diminishes the amount of power a demon can exhibit.

Not all possessed are unwilling however. Sometimes a depraved or power-hungry individual makes a pact with a demon to share their body with the demon. This allows the Demon to enjoy it's full potency (obviously without the benefits of sharp claws or wings).

When in possession of a being's body, a demon cannot vacate them and assume it's regular form without a careful and elaborate ritual. Usually killing the host will result in the temporary destruction of the demon as well; with some rare exceptions.

Due to the difficulty in vacating their hosts, and the decreased potency of their powers while possessing a host, the Tomerian Order "Wardens of the Damned" track down and confine Demons while they are possessing a host. If a host isn't around, they will have a brave volunteer sacrifice him or herself and bind the demon as it's host.

Demonic Form
Most Demons live trying to balance a difficult tightrope. It is in their nature to seek out and be among mortals, however to do so they must possess a host to navigate society. Being around mortals allows them to influence, corrupt, torment and murder as much as possible. But as stated, possessing a host is a difficult and draining thing for a demon. As a result, many Demons will collect a coterie of followers, cultists, admirers and hanger-ons while possessing a host. They will take these followers out away from prying eyes, and use them to perform a ritual to shed their host. Returned to their form and with a collection of fools to torment, they will spend decades slowly using up their followers until one remains. Typically they will possess this figure, and return to mortal society to collect more.

Often, demons will band together under the leadership of a powerful Demon Lord. They will take up residence in dusty dungeons, dark deep caves, ruined cities or other secluded locations. While there, they will send out bands of demons to collect slaves, hosts to trick followers to come to the demon lair, and accumulate treasure and relics.