"Githyanki first visited Athas long ago aboard a vast, silvery craft that transported them from a place beyond the Gray. The githyanki sought a way back to their realm, but they found themselves trapped on Athas by the Gray, which serves as a nighimpassable planar barrier between the world and their home realm. Meanwhile, the visitors proved particularly sensitive to the corrupting nature of arcane magic. Today, the descendants of the first githyanki survive as shadows of their former selves, decayed in both mind and body. They have not forgotten their origins. however. A few tribes are dedicated to gathering shards of their long-lost ship. hoping to return home." - Dark Sun Creature Catalogue
Although it was dropped in the 4th Edition ravamp, their original reason for travelling to this world, and their fall, was because of a war with a sister race, the Githzerai. Their current state was because of experimental weaponry used by the Githzerai, which backfired, and drove them all mad. Also not mentioned, but they are reptilian, including laying eggs. They sometimes allow creatures called Belgoi into their tribes to act as shamans, which is odd, because Belgoi are fey creatures obsessed with bells, and seem to have no real connection to the Gith.
To paraphrase, the Gith are a race of degenerate, latent psychic humanoids who have completely lost their culture and history due to some ancient and tragic war. While it is easy to play them as typical monstrous humanoids, I like to imagine them less as just a reskinned Orc for the setting, and more dangerous creatures to be pitied. Here is my take on them.
The Gith are degenerate humanoids, cut off from their culture for thousands of years. Nearly the entirety of the knowledge they have of their own history is the language they speak, Deep Speech, the language taught to them when they were slaves at their races beginning. They seem to know that they are missing their history, but either through lasting damage from the Githzerai gene bomb, inbreeding or simply countless centuries living on the surface of Athas, their brains are withered and their minds atrophied. I imagine them acting like someone with a degenerative brain disorder like Alzheimer's or dementia. Their actions are erratic and unusual, and they intrinsically know that something is wrong with them. They have moments of lucidity, but for the Gith, these are times of melancholy and horror, as they look upon their brothers and sisters and wives and husbands (often the same people) and know, just for a moment, the horror of their existence.
I like the imagine them inhabiting ruins set into the sides of canyons. Stolen fabrics are draped across their homes, and they smear ink, pigments and dyes across the adobe walls in abstract and clumsy patterns. Food lies rotting in cracked ceramic, and their few gardens are ill kept and weedy. Giths with burning brands explore the deep recesses of the ruins, looking for books and scrolls to keep their watch fires burning at night. They are not malicious by nature. They are as likely to throw rocks and hoot like apes from above at those passing through their canyons as they are to descend on them with obsidian tipped spears.
They hoard objects that remind them of their history. Silver and verdigris are treated with reverence. Astrolabes, sextants, and any objects used for navigation are likewise treated as holy objects. Many of them use abandoned shrines, worshiping gods with no concept of who that deity is, or desecrating the shrine and replacing the iconography with a mishmash of scavenged symbols.
Next time your player's encounter Gith on the wandering monster table, consider giving them a strange and savage superstition.
- Sometimes the Gith breed true. This tribe has an altar dedicated to a living saint: a child that is indistinguishable from a young Githzerai. He has not been allowed to leave the shrine since his birth, and is weak and anemic. His eyes can only stand the dim light of candles. Upon the child's tenth birthday, he will be dragged out into the sunlight for the first time and burnt on a ceremonial pyre.
- The Gith believe that if enough mirrors can be brought together, it will return them to their home. They lack the ability to explain why, but they covet mirrors and pieces of polished silver, which they lay out inside of an old building to make a huge mosaic.
- The Gith desperately collect copper, because they believe that verdigris is a sacred color. The highest member of the tribes wear as much copper as possible, and they believe that copper pieces are the most valuable type of coin. Their leaders have carried the same broken and green copper sword for generations, and they believe it was carried into this world by the first of their kind.
- The shrine of this tribe contains the figurehead of a sailing ship. They no longer remember where it came from, but they meticulously oil it to keep it safe from burrowing insects and worms. It is the totem of their tribe, and their shaman places his ears to its lips to hear secrets and spells.
- These Gith obsessively steal from a local church or monastery. They collect as much religious iconography as possible. They snap the crosses off of tombstones, wrench symbols off of walls, but have so far have only been an annoyance to the clergy. These stolen symbols are believe to contain powerful magic, and so they are carried by the tribe's shamans and used in improvised or mimicked rituals.
- The Gith believe that their form is a curse, and so they try to act as civilized as possible. They stand as tall as they can despite their crooked spines, bathe constantly, and use perfumes. They try to copy the dress of travelers in their region, and can sometimes be seen acting out elaborate, ritualized versions of everyday life among other races, such as meticulously serving food on plates, or building chairs out of bones and twine.
- These Gith follow a shaman who is obsessed with divination. Each morning they gather around to hear his proclamations, and the refuse to believe that he could be wrong. These Gith will follow the players and attempt to discern if they are a part of the days prophecy. They may follow at a distance, meticulously counting the steps the players make. They might leave groups of objects in their path to see which thing they pick up first. Eventually they grow weary of the tests, or the players will fail according to their inscrutable logic, and the Gith will descend upon them with spears and knives.
- This tribe has a Belgoi shaman living amongst them. The two species lack a common language, but the Gith have a great amount of respect for the fey, and are attempting to mimic it by carrying bells and chimes. Bells are known to carry great magic, so warriors walk around with as many bells tied to their wrists and ankles as possible, and the tribe's arrival is always heralded by a cacophony of bells. The Gith will not attack any town that sounds a church bell.
- These Gith are deeply ashamed of their hairless bodies. They scalp their kills and weave them together into cloaks, which they wear at all times despite the heat. Their tribes leader wears, and keeps meticulously groomed, an all blonde cape of which he is inordinately proud. From a distance, the hunting parties of this tribe appear to be a herd of yaks.
- After capturing a silk merchant, this tribe has a plethora of colorful fabrics. After some initial confusion about the meaning of the colors, it quickly became obvious that the colors are signification of rank. Or possible clan allegiance. It's gotten a little confusing, and the entire Gith village has been locked down in a weird cold war, as they attempt to avoid having to interact with Gith wearing clothing that is not the same color as the clothing they are wearing. It has gotten so bad that were adventurer's to enter the village, each color would not lift a finger to help another, although to adventurer's in a sword fight, the clear difference between indigo and violet might seem inconsequential, leading to temporary alliances between colors.