Sun Mar 15, 2026 1:30 pm  
A Brief History of the Yuan-Ti (by Samwise)

This summary was posted by Sam “Samwise” Weiss on CanonFire Discord and was too good to be lost to posterity:

A Brief History of the Yuan-Ti

The Yuan-Ti first appear in I1 Dwellers of the Forbidden City. Their background is exceptionally lean, merely noting they had been human and were turning into snakes. This was continued when they appeared in Monster Manual 2. At this time, while they had psionic attack and defense modes, they did not have psionic powers. Their abilities were overtly described as casting spells.

In Dragon 151, "The Ecology of the Yuan-Ti" appeared. They were given an origin and a patron, the demon lord Sch'theraqpasstt (pronounced schikthere-AUK-past). In that article, they are humans who were into the demon, who "rewarded" them by giving them the alchemical poison that creates hisstachii "broodguards". When hisstachii do the nasty, they produce yuan-ti purebloods, who then produce half-bloods, and then abominations. Sch'demon tried to merge with his Abyssal layer and went insane. Some yuan-ti want to restore him.

In 2E, yuan-ti originally remained the same without psionic powers in the Monstrous Compendium. In Monster Mythology, Merrshaulk is presented as the patron of yuan-ti. Merrshaulk is presented as a fading being, spending most of its time asleep, curled up with Ramenos, patron of the bullywugs. In general, aside from hanging out together, the descriptions have a resemblance to Yig and Tsathaggoa of the Mythos, both being generally fading, into drugs, and interested in little more than eating when the sacrifices their cultists give them. Monster Mythology is dated 1992. Monster Mythology also introduced the World Serpent, which gets very complicated later on.

This is where things get a bit ginchy.

In the Complete Psionics Handbook, the yuan-ti are given a suite of psionic powers in addition to their spell abilities. This is carried into the Monstrous Manual, the replacement for the ring-binder Monstrous Compendiums. CPH is 1991, before Monster Mythology, Monstrous Manual is 1993, after Monster Mythology.

In 1996, The Vilhon Reach came out for Forgotten Realms. Yuan-ti feature in this, and it is around this time that various elements of the World Serpent are developed in FR and Planescape.

In 1998, Scarlet Brotherhood comes out, with a completely different, Olman, origin for the yuan-ti.

3E features another bout of expansion and divergence.

In the Monster Manual, the yuan-ti have psi-like abilities instead of spell-like abilities. When the Psionics Handbook and later Expanded Psionics Handbook come out, they get fully psionic options for these abilities.

The yuan-ti get some more expansion, first with tainted ones appearing in the Faerun Appendix to the 3E Monster Manual, and later a massive expansion with Serpent Kingdoms, which heavily develops the World Serpent concept for FR, syncretizing and combining several powers. Merrshaulk is big, Sch' is barely mentioned.

Some other additions to the yuan-ti show up in Savage Species and later Monster Manuals.

Late in 3.5, Sertrous is invented as an obyrith lord. He appears in Elder Evils and the three part Vanguard series of modules. Sertrous originally had a different focus, got smacked around by the Queen of Chaos for refusing to join her war, and took the form of a serpent to survive. Sertrous stared sending plagues of serpents to destroy temples and followers of the powers. The powers sent a solar to teach Sertrous a lesson. Sertrous was beheaded, but his head spoke words subverting the solar and setting in motion the first thing about getting clerical powers from serving abstract concepts rather than specific powers. One might connect to this the ur-priest class from Book of Vile Darkness as well. The solar fell and stole the head of Sertrous.

Curiously, Pathfinder has Ydersius, a patron of the Howard inspired serpentfolk of Golarion, who was also beheaded. Pathfinder also had Yig as part of a Mythos-pantheon.

No idea about 4E and 5E revisions.

Overall, yuan-ti psionics was, in fact, a later retcon/addition. They had default attack/defense modes like a lot of creatures but were not inherently or notably psionic. Re-retconning them to purely magical is not that big.

For origin and patron, that is a mess. The first version elaborates on the human corruption element, but that patron was dropped in 2E, probably because it was from a Dragon article.
The 2E patron was decadent and fading, like the yuan-ti, and with no specific creation story.
The GH creation version stepped in later. I am not familiar enough with FR, but it might predate the FR sarrukh origin.
The FR origin, which because of the usual factors, became dominant, is entirely different, and technically mortal but with adopted divine patrons and the World Serpent concept hardwired in.
3.5 introduces yet another alternate patron that seems ex-post facto, and with another focus.
Mythos influence shows up in the 2E version, though how that carries forward cannot really be locked down.

Overall, almost anything can be done with them at this point.