The cult of demise collects souls. They do not seek out living beings, but rather recently passed individuals. There are only ever four in the Council. Each member contributes to the collective of souls that circulates throughout the world, essentially they act as distributors of the Essentia magic. When a member is destroyed, they are replaced by the rest of the cult by seeking an individual who has died by the hands of another, whether it be a mage or an animal.
The cult members wear the skull of the animal or person that killed them. They store and siphon Essentia magic from that skull.
Essentia magic is what keeps this cult alive, and thus they have mastery over it. Their ability to will weapons out of souls gives them an edge over most other magic and non-magic users, except those who carry mirra-objects. Based on the souls they have collected, their particular weapons have specific ailments that affect targets in various ways, such as stunning or poisoning the victim. If an essentia-weapon strikes through an enemy’s bone, part of their soul (essentia magic) is taken.