Three-Faced Sun heresy

The Three-Faced Sun heresy was the idea that the sun was an overdeity. According to this heresy, this overdeity had a total of three aspects out of which two were eligible as objects of worship by mortals, the ones of with two aspects that were eligible as objects of worship in the form of deities.

Believers in this heresy claimed that Amaunator and Jergal were the aspects of highsun and dusk respectively during the days of Netheril. Later, these positions were fulfilled by Lathander, as the aspect of dawn, and Myrkul, as the aspect of dusk. After the Time of Troubles, the Morninglord, according to this heresy, experienced a time of unchallenged authority.

Break Down
A substantial part of believers in this heresy claimed in the 1374 DR that the Morninglord was close to transform into the Yellow God. However, a minority believed that Lathander was about to take over the position as the high sun-aspect, essentially handing over the dawn-position to another deity, while another minority believed that a completely different god would ascend to take over the position as the high sun-aspect.

Powers
Clerics who believed in this heresy were capable of accessing the Death, Law, Renewal, Sun, and Time domain. They could use both the light mace and the scythe as their favored weapon and could add the flaming quality to either of them on casting weapon of the deity.