Dark Moon heresy

The Dark Moon heresy was the belief that Selûne and Shar were two aspects of the same deity. Believers of this doctrine could be found teaching it to others.

Origin
The Dark Moon heresy was originally a scam made up by Alorgoth to lure less than unwavering worshipers of both Selûne and Shar, his goddess, to one place, the Twofold Temple, and kill them all there.

Followers' treatment by the deities
As mentioned above, those who believed in the Dark Moon Heresy held that Selûne and Shar were two faces of the same goddess. While all followers of this heresy weren't allowed into either goddesses' realm on death and were judged False, Alorgoth was apprently onto something with his lie for clerics who supported this heresy were supported by the two - or according to them one - goddess with full access to both churchs' spells and permission - so to speak - to grossly violate the two churchs' tenets.