The yuan-ti trace their origins deep into the misty past where an alliance of nagas and couatls created them as additional help in guarding various important supernatural locations and objects. Infused with the essences of their supernatural progenitors, yuan-ti are gifted guardians and protectors, and many still serve in those roles, either for their original patrons and creators or for others who have need of competent watchers.
All yuan-ti share a few basic traits: a serpent-like body plan with humanoid arms, innate magical talent,and the ability to sense magic, but beyond this common baseline, they are a wildly diverse people. Some have more humanoid heads, while others are unmistakably snakelike. They can be colorful or drab, and can have fangs, cobra hoods, tail rattles, and even wings depending on whether they take after their people’s naga or couatl influences more. They have the same variances in height, musculature, and body mass as any other mortal. Some have humanoid hair, others scaly frills, others plumes of feathers. And like any mortal, they can be cruel or kind, individualistic or cooperative, flighty or responsible, gregarious or reserved, serious or playful.
Though it is still very possible to find large communities of yuan-ti maintaining their ancient vigils over shackled elder evils, magical artifacts, dimensional portals, and other places of power or religious significance, as time has passed and the yuan-ti population has grown, more and more have left their ancestral homelands and integrated into the wider mortal population or formed communities of their own, away from any specific thing to be guarded. Most large cities have at least a few yuan-ti living in them, and while their natural gifts often guide them toward careers involving magic or security in such a cosmopolitan environment, they can be found in as wide an array of professions and lifestyles as any human, elf, or gnome. Because of their origins, other mortals often tend to view yuan-ti with the same kind of regard they would a naga or a couatl: likely benign, but also a strong indicator that something very powerful (and often dangerous) may also be nearby.
Characters with the yuan-ti heritage share a variety of traits in common with one another.
Age. Yuan-ti mature at about the same rate as a human, reaching adulthood around age 20. Their supernatural essence makes them extraordinarily long-lived, however, with most living well into their 800s and a few living to more than a thousand years old.
Size. Yuan-ti have human-sized torsos on long, serpentine bodies that stretch 20 feet long or more. They usually weigh at least 350 pounds and sometimes as many as 600. They can coil themselves up to not occupy much more space than a human, however. Your size is large, but you use medium-sized equipment and can comfortably move through most spaces designed for medium-sized creatures.
Speed. Your base speed is 30 feet. Serpentine Physiology. Your lower body has the shape of a massive, powerful snake. This grants you the following advantages:
Magical Sense. You know the detect magic spell and can always cast it as a ritual.
Supernatural Origin. You know a cantrip from the following list: mage hand, prestidigitation, spare the dying, or thaumaturgy. Your spellcasting ability score for this cantrip is Intelligence, Wisdom, or Charisma (whichever is highest).
Yuan-ti are highly-varied and diverse even within the same family tree. In addition to the traits found in your yuan-ti heritage, select one of the following yuan-ti gifts.
Some yuan-ti have exceptionally muscular tails and heavy, armored scales. They tend to also have muscular torsos and scales on their upper bodies. You have the following traits:
Scales. You have tough, plate-like scales. While you aren’t wearing armor, your AC equals 13 + your Dexterity modifier. You can use a shield and still gain this benefit.
Constrict. You gain an expertise die on checks to initiate or maintain a grapple on creatures of Medium size or smaller, which can be coiled around as part of the grapple. Once per turn as a bonus action, you can squeeze a grappled creature in your coils, dealing bludgeoning damage equal to 2d4 + your Strength modifier. In addition, your hands remain free when you are grappling another creature. You cannot use your climb speed from Yuan-ti Physiology while using this trait. You cannot coil around creatures of Large or larger size.
Some yuan-ti have dagger-like fangs and venom sacs. These yuan-ti are likely to have viper-like physical traits such as a cobra’s hood or a rattle on the end of their tail. You have the following traits:
Venomous Bite. You have a venomous bite. As an action, you can attack with your bite (which is considered a finesse weapon) dealing piercing damage equal to 1d4 + ability modifier and poison damage equal to 1d4 + your proficiency bonus.
Rapid Bite. You can also bite much faster, forgoing the opportunity to inject venom. You may make a bite attack as a bonus action, dealing 1d4 points of piercing damage + your ability modifier (but no poison).
Poison Resistance. You are resistant to poison damage and have advantage on saves to avoid the poisoned condition.
Menacing Viper. You gain proficiency with the Intimidation skill.
Some yuan-ti take strongly after their couatl progenitors and grow feathered wings. These yuan-ti are more likely than most to have colorful scales and feathers on other parts of their bodies such as a feathered crest on their heads or shoulders. You have the following trait:
Flight. You have a fly speed of 30 feet. To use this speed, you can’t be wearing medium or heavy armor. Whenever you spend 3 full consecutive rounds airborne without landing, you gain a level of fatigue. Any fatigue gained in this way is removed upon finishing a short or long rest.
With enough time and training any yuan-ti can unlock their full serpentine potential. When you reach 10th level, you select one of the following paragon gifts.
Prerequisite: Constrictor heritage gift
The damage dealt by your squeeze increases to 2d8 + your Strength modifier. In addition, if a creature you have in your coils is bloodied, it cannot breathe and must hold its breath or begin suffocating.
Prerequisite: Viper heritage gift
Your venom has become some truly nasty stuff. The poison damage of your venomous bite attack increases to 1d8+ your proficiency bonus and a creature taking this damage must make a Constitution save against a DC equal to 8 + your proficiency bonus + your Constitution modifier or be poisoned until the end of its next turn.
Prerequisite: Viper heritage gift
You gain the ability to spit blinding venom at your foes. Your venom spit is a ranged weapon attack with a range of 40 feet. If you hit, the target suffers 2d6 points of poison damage and must make a Constitution save against a DC equal to 8 + your proficiency bonus + your Constitution modifier or be blinded for until the end of its next turn.
Prerequisite: Viper heritage gift
Your venom has become infused with holy power. Your venomous bite attack now deals an additional 1d4 points of radiant damage on a hit, which increases to 1d8 against aberrations, fiends, and undead. In addition, you learn the venomous succor spell and can cast it once per long rest without using a spell slot.
You select a second Yuan-ti Gift, gaining its benefits as normal.
Prerequisite: Winged Serpent heritage gift
Your fly speed increases to 40 feet and you can fly while wearing medium or heavy armor. When you would suffer fatigue from using your fly speed, you make a Constitution saving throw (DC 10 + 1 per previous save in the last minute). On a success, you do not suffer fatigue from flying that round.
Yuan-ti society has historically been oriented around guarding something, but what that thing is and what that guardianship looks like has varied significantly since the earliest days of the existence of the yuan-ti as a people. Some yuan-ti communities have been given the grim task of making sure something dangerous or evil such as a powerful monster or evil artifact stays locked away where it cannot harm the world. Others have been tasked with making sure something beneficial such as a magical healing grove stays safe and available to those who need it.
Yuan-ti communities tend to be good neighbors, trading fairly with others and helping when they can in crises. This is often simply out of genuine friendliness and compassion, but the yuan-ti also know that their missions are orders of magnitude easier when they are surrounded by friends rather than enemies.
This society-wide sense of weighty responsibility has tended to make yuan-ti from traditional guardian communities into serious and vigilant people and also ones that value trust and harmony in their lives. They typically work hard to resolve internal disputes fairly and amicably. Responsibility for ensuring the world doesn’t end means being able to trust and rely on your neighbors is a tremendous asset, and nobody knows this better than the yuan-ti. Yuan-ti of all stripes tend to be very forthright and straightforward communicators as well, with little subtlety or subtext in their words. If a yuan-ti wants something from someone else, they will typically just ask and if they value or are bothered by something, they will say so. This is not to say that they cannot lie or that their words are a stream of consciousness or lacking in nuance, but they don’t tend to be very subtle or manipulative as a rule.
A significant number of yuan-ti have left their traditional guardian roles behind, often with no animosity involved in the decision; because of their long lives, a community of yuan-ti will often eventually reach the point where further population growth becomes more of a liability than an asset where maintaining a vigil is concerned. When this occurs, they encourage those in their community interested in exploring the wider world to do so, regardless of their station or age. Yuan-ti who leave these guardian communities (or those descended from those who did) generally fall into one of two categories: those who left in groups to establish new communities somewhere or those who left on their own to chart an individual destiny. In all but the most extreme cases, they are typically welcome in their old communities whenever they choose to visit.
Yuan-ti who leave in groups tend to establish societies in places that have warm climates and an abundance of ambient magical energy, both of which yuan-ti find comfortable. This leads many to set up in deserts or swamps, to the point where desert yuan-ti and swamp yuan-ti have developed adaptations particular to their chosen biome over time. And more than once, one of these communities has wound up watching over some important or dangerous thing that they discovered in their new home region.
Those who leave on their own often gravitate to large urban centers; a yuan-ti’s natural sense for magic often leads them to a role in a city watch or magical institution of some sort, such as a wizard college. Their connection to couatls often means they are especially welcome in religious institutions as well, but ultimately, they are as versatile as any other mortal and their long lives mean that many often have more than one career over the course of their life. The yuan-ti have produced artists, musicians, tradespeople, soldiers, scholars, mages, clergy, and members of every other profession.
While you can choose any culture for your yuan-ti character, the Ancestral Guardian, Desert Yuan-ti, and Swamp Yuan-ti cultures are especially linked to the most common yuan-ti experiences. Those who are part of a group that has recently forged out on its own often have the Itinerant, Nomad, or Settler culture. Those with more of an individualistic bent are most frequently Cosmopolitan, Steamforged, or Lone Wanderers.