Cult of the Dark Heart

The Cult of the Dark Heart is a faction of rogue former Ashari who are allied with the Ruby Vanguard.

Campaign 3: Bells Hells
When Bells Hells first met Keyleth when she transported them to Whitestone, she mentioned she was dealing with a "rogue faction" based in Issylra. Some time later, Orym asked Imogen to check in with her, and Keyleth mentioned that she was dealing with something dangerous beneath Terrah near the rift to the Elemental Plane of Earth. She surmised it might be related to the Vanguard's plans for the apogee solstice.

A little over a week later, she sent Orym a message via the Message Bloom he had received from Niirdal-Poc, telling him she and others had dealt with a Dark Heart Behemoth and stabilized the rift, but that Vureeo, leader of the Cult of the Dark Heart, had escaped, saying that "the Vanguard will prevail."

Trivia
Hishari was the home of an elementally-affiliated cult that shares part of its name with that of the Ashari; it is not yet known if that cult was the Cult of the Dark Heart.