The Curse of the Transformed Soul

A simple but terrifying spell, The Curse of the Transformed Soul permanently changes a person into being any other sentient being the caster wishes.

Effect

This occult curse allows the caster to alter the person being affected, changing them into any species or gender. With care and precision of the caster, they can even create an exact vision of the intended appearance of the new look, especially useful if the caster is particularly vindictive.

Side/Secondary Effects

The affected person's whole body is altered, including their voice. Their vision and hearing also changes, meaning former humans turned to Orc or Drow can now see easily in the dark as they once did in the day.
The curse has profound effects internally, and is thought to alter the very nature of someone's soul. A person who has been altered from one species to another can theoretically conceive children with a partner of that new species. This would not normally be possibly; as interspecies unions never result in pregnancies, so merely altering the appearance of someone would not achieve this affect.
The spell is so effective and complete that attempts of scrying to detect illusions or deceptions do not detect it: it is as if they have been entirely replaced with their new selves.

Source

Where the power to cast such a spell is not fully known, but it is fully of the occult. No arcane student of wizardry, nor any holy cleric or champion has been able to replicate the spell or its effects, though some illusion spells can mimic them.
The effects carry all of the familiar marks of the Fey, the chaotic beings who altered the very world to their maniacal glee. Even the Witches and other casters who deploy such spells are not fully aware of the nature of the higher powers they make their bargains with. If any Witch were knowingly making deals with those who sought to destroy the very existence of T'sara, none would be fool enough to make it known.
Some have thought the spell could be replicated, or at least undone, through the holy powers of Khalee, Goddess of Beauty. They have made it repeatedly clear that their clerics possess no such power, and that they would never permit it through them. Such a request in fact goes directly against Khallee's central tenant of philosophy, that "there is beauty in all things".

Discovery

The first documented case of the curse being used exists in folklore. A Halfling trickster and Witch by the name of Rumumuck had encountered a vainglorious, obnoxious, and filandering human hunter. He would never stop pursuing and accosting the elvish women of the city, harassing them with lewd and sexually evocative language, pressuring them constantly to let him take them to bed. Having asked the hunter Gasyl to stop, and having warned him that there would be consequences should he not, Rumumuck turned him into one of the very Elvish women he constantly sought after. Granting the "gift" of radiant beauty, Gasyl would long suffer the same harassment and behavior he inflicted.
Stories vary wildly in mild details, including the names of the characters and to what the victim was turned into, although the core of the story remains consistent. Where the tale deviates the most is in the ending; some written with a more optimistic tone say that the hunter begged for forgiveness and was turned back, having fully learned his lesson. Others leave the consequences ambiguous, ending shortly after the hunter has been transformed and realizes their fate. A curious variation of the story tells that the hunter never returned back, but eventually actually became happier in their new form than they ever had before they were cursed.

Material Components

There are no material components known as needed to cast the spell, though it does appear to change from one caster to another, who they bargained their power with and how. What is critical is that otherworldly bargain; the access to the occult spells and power not of T'sara. Without it, the spell may never be cast.

Gestures & Ritual

Though not needed, some have incorporated ritualistic and religious ceremony into the spell. A contingent among the Tribes of Krag'ash have spiritual leaders who've made the witches bargain, and involve the whole of their tribe in the casting of the curse.

Applied Restriction

Such a powerful curse is generally thought to be permament, having worked so thoroughly to alter the person affected by it. However, like in the story of Rumamuck the Trickster, there are cases where the curse is broken, either if the person cursed meets certain conditions established when the curse is cast, or if the witch chooses to voluntarily break it.
There are tales of people seeking out witches to have this spell deliberately cast upon them, desiring vehemently to become another gender, or even a different species. Using their position of power for leverage, it is not uncommon for the witch to exact a bargain of their own, extorting a favorable agreement the affected must adhere to, lest the spell be broken.
Some stories tell that the curse is broken upon the death of the witch who cast it. Given that these are often folklore tales of daring heroes, and not historical records, there is often a great deal of skepticism; believing instead that it's merely a vehicle of the plot for a 'happily ever after'.