Merrshaulk

Merrshaulk was the chief god of the reptilian yuan-ti, a chaotic evil mastermind of traps, poison, and murder. His clerics were known as vrael olo. His symbol was a flying snake with bared fangs.

History
Like all the other gods of Toril, during the Time of Troubles, Merrshaulk was cast to the Prime by Lord Ao. He appeared over the jungles of Chult as an enormous magic-using winged snake, exhorting his priests to gather their strength. But as he slept in his lair, he was bound by the Mulhorandi god Set into a magical captivity in the Abyss. The Father of Jackals then usurped his portfolio and thereafter granted spells in Merrshaulk's name.

The vast majority of yuan-ti were unaware of this; those who knew something were vaguely aware that the Slitherer Supreme was distressed in some way. Set's binding upon the yuan-ti god was imperfect, and fragments of nightmares sometimes appeared in visions to his followers. Those who saw them generally interpreted the dreams to mean that Merrshaulk was upset or angry. Repeated divinations determined that Merrshaulk was in distress of some sort, prompting many yuan-ti to quest for answers.

A small minority of Merrshaulk's followers learned a partial truth, that their god was losing a battle with another, and that the Okothian sarrukh were to blame. Those who knew this kept it quiet, hoping to gather more information on the matter before revealing it. The Okothian sarrukh knew the full truth, but were sowing disinformation among the yuan-ti to delay and confuse any investigation.

If Merrshaulk was ever freed, he would likely declare war upon the Mulhorandi god, and (possibly) ally himself temporarily with Set's foes.