Clerics worship Gods for there magic, but what would happen if a got refused to grant a clerics magic? Normally not much but when the soul becomes angered by the god's refusal they become an accursed. An accursed is obsessed on spreading misfortune. Their flesh twists and there eyes go pale, the arcana is forced through the body granting  supernatural afflictions and loss of any intellect they had, but still, no real magic.