The cultists were told lore of the days of ancient light, when the sun used to emanate light by the priestess of the Black Sun.
The gods of this planet wanted the souls of the wicked to come to their planetary conception, so they darkened the world. When she said such strange things, she would transform her staff into a snake and suck the venom of it to alter the flows of her mind to access the words of the gods. She lived in a cave, with a curvy stairway descent to her sleeping place, with arcane symbols written on the walls in radiant, purple paint. In awakened hours she would talk about her prophetic dreams given to her from the gods of what may impend on the earthly realm.
One of which was about grotesque beasts which had a malign intent to desecrate the gods in the kingdom of the blackened sun. It was a disconcerting prophecy to utter the least. In no time the prophecy came into play and rivalries begun and the priestess did alluring chants to awaken the slumbering ones in the deepen ground to assist the battle. The strange opal jewel on her staff would absorb energy from the blackened sun and emanate it at the foes and decimate them into dust. After mighty valour and battle woe, they became victorious in the realm of the blackened sun.