Merrshaulk

Merrshaulk
Alignment	Chaotic Evil
Divine Rank	Intermediate God
Pantheon	Yuan-ti
Portfolio	Beasts, Predators, Somnolence
Domains	Animal, Chaos, Charm, Destruction, Fate, Plant, Scalykind, War
Home Plane	Smargard, 74th layer of the Abyss.
Worshippers	Yuan-ti, Hunters
Favoured Weapon	Longsword

Merrshaulk is one of the main deities of the Yuan-ti species in the core D&D setting, but in the Forgotten Realms setting, Merrshaulk is just one in a line of snake deities since they tend to fall asleep and get replaced.

History

In the beginning, there was just one deific overbeing: the World Serpent, (called "Mok'Slyk" in the Greyhawk setting) which for D&D is practically the Ouroboros, a creature of incalculable and eternal power on a scale similar to the Lady of Pain or Ao and was worshipped by the progenitor races.

Over time, those ancient empires fragmented into smaller kingdoms who brought unique aspects of worship with them, breaking the World Serpent into smaller deities, forgetting the original World Serpent and depriving it of power to the point that it no longer grants spells or answers prayers. In fact, the only being suspected to have any contact with the old "Serpent" is Vecna, who was supposedly trained by it. Though that may very well be just some mad ramblings.

Merrshaulk was the aspect of the World Serpent who took the portfolio of actual snakes and is worshipped by the Yuan-ti. Furthermore, Merrshaulk is a particularly nasty deity who demanded constant sacrifice, preferably willing Yuan-ti, but content to accept unwilling prisoners from other races if provided in bulk.

Sseth

Sseth
Alignment	Chaotic Evil
Divine Rank	Intermediate God
Pantheon	Yuan-ti
Portfolio	Poison, Secrets, Somnolence
Domains	Air, Animal, Chaos, Evil, Knowledge, Magic, Planning, Scalykind, Trickery
Home Plane	Smargard, 74th layer of the Abyss.
Worshippers	Yuan-ti, Scalykind
Favoured Weapon	Scimitar

In the Forgotten Realms, Merrshaulk has been replaced by Sseth, the Slitherer Supreme.

During an early period of Faerun's history, Merrshaulk had grown tired and bored, and started forgetting to answer prayers or grant spells. Quite possibly because the rate of sacrifices offered had slowed to a trickle because younger races were starting to form their own empires and openly fighting back against the Yuan-ti.

Then one day, a winged Yuan-ti with a talent for giving speeches showed up and declared that he was the avatar of Merrshaulk reborn and that the Yuan-ti should start worshipping him instead. So when faced with the fact that this new guy would grant their spells and sleepy old Merrshaulk would not, the choice was clear.

Sseth was also probably a better deity politically compared to his predecessor. While the new guy still demanded a constant flow of sacrifices; where the old religion was very primal and focussed on survival and animalistic hunger, Sseth by contrast was a god of secrets and intrigue. His rewards would be whispers of knowledge to grant advantage and further ambition.

However, some Yuan-ti disliked the new direction the church went in, finding it too decadent and indulgent and choose to continue worshipping Merrshaulk anyway, even though he doesn't actually answer prayers.

Set

Set
Alignment	Lawful Evil
Divine Rank	Intermediate God
Pantheon	Yuan-ti, Mulhorandi, Phaeronic
Portfolio	Deserts, Disease, Drought, Darkness, Betrayal, Ambition, Murder
Domains	Air, Darkness, Evil, Hatred, Law, Magic, Scalykind
Home Plane	Heliopolis.
Worshippers	Yuan-ti, Lycanthropes, Egyptians
Favoured Weapon	Spear

Just like his predecessor, Sseth also became bored and sleepy, although he still granted spells even in his dreaming state. That was up until the Time of Troubles in the realms, where all of the gods were kicked out of their respective realms and forced to the mortal world until one of them owned up to stealing the tablets of fate from Ao.

During this time, the winged avatar of Sseth decided to go for another nap, but was captured and imprisoned by another evil god of snakes called Set, who now grants all spells in Sseth's place, even though the Yuan-ti have no idea that the switch actually occurred.

Set; being a "human" deity obviously has far more followers than Sseth, and more widespread appeal. Meaning that Set is likely to have more of a meaningful impact on the world than the successive serpent deities were managing to cobble together. He also has the added bonus of not following that trap of getting tired when sacrifices aren't being given, although presumably he's extremely happy to receive the bloody offerings whenever they're given.

Sseth still sleeps, hidden somewhere in the multiverse. His extent of contact with the outside world is an increasing number of disturbing visions being granted to his former followers in their dreams, though most of them don't have a clue what they're all about, other than getting a sense that their god is in trouble. Because his portfolio has been usurped it is likely that he won't last for very long, because gods thrive on the power of prayer and faith, so Sseth is likely getting starved to death. Those Yuan-ti that have the power and inclination to do anything about it simply don't know where to look, smarter Yuan-ti realise that their power and ability to look is being granted from a new source which probably doesn't want them looking in the first place.