Demons and other spirits
Demons are one of the most feared creatures in all of Severil. Spirits from the elemental chaos, they are often summoned by ambitious mages looking for power.demons in spirit form are mostly harmless, though some can amass enough strength to be a threat without a body. As a spirit, they are unable to affect the physical world. The true danger is when they possess someone. When they enter a body, the current soul and the demon struggle for dominance. If the person wins, they gain some semblance of control over the demon. If the demon wins, he consumes the souls and transforms the physical body into a powerful aberration. After the possession is complete, the demon is free to do what it will, which is usually create havoc. A demon is extremely hard to kill once it has possessed someone, as it has exceptional physical and magical strength.
Summoning spirits is an offense punishable by death, as a demon is very hard to control and the magic used to summon them must be extremely precise. As such, only the most depserate or power-hungry mages attempt to summon them.