There is no specific cult group, there is no one false god they worship. The use of magic depends on how a person perceives the world, if they deny the existence of the Ever One that life has no meaning and all actions are just a cause of chemicals in the brain, they are more subjective to magic, and are more specifically targeted by nightmares, because of their denial.
Those with fears can be more susceptible in a circumstance when faced with their fears.
People that believe they are untouchable or unbeatable are more susceptible to failure and sometimes will fall into depression from which they cannot escape.
Revenge burns bright at first, they hate allowing them to defy magic, but only lasts till their revenge has been satisfied, and with nothing to drive them they slowly fall into depression.