This blog entry is based on the "curse as a class" entry by Bubbear Slug: The Abattoir God. I highly recommend you read it, but the tl,dr is this: A human is "chosen", slowly gains powers and becomes the Abattoir God, only to be later slaughtered and sacrificed by the cult members. A new one is then chosen - usually from among the cultist, but sometimes a random stranger.
This idea is too good to pass up, and here is how it would fit in Yoon Suin.
The Abattoir God's cult is ancient, and has its roots in Occidentalia, that mythical land far to the west. Its history is intimately tied in with the history of ogre-mages. The flesh of the Abattoir God is potent, and while the cultists eat much of it, they can raise significant funds by selling some of it to others. They also know that a member of the cult is not always chosen, and thus it is essential that outsiders also have access to the God-Flesh - only someone who has partaken in the Divine Flesh can be chosen to become the next Abattoir God.
About 1500 years ago, a mage, seeking to create a powerful servant, served head-cheese crafted with the brains of the sacrificed Abattoir God to an ogre. Pleased with the results, he repeated the experience. His two ogre servants, far cleverer and even tempered than a standard ogre, learned magic from him and served him well for several years. After a dozen years, they convinced them than a third member would serve him even better. They observed the procedure carefully, and after learning the secret, slew their master and left town with the third ogre. Thus was born the first three ogre-mages.
Knowing that God-Brain was essential to their propagation, one member infiltrated the cult while the other two worked to raise funds and located ogre candidates. During the next sacrifice, they purchased the entirety of the brain, and the number of Ogre mage jumped to almost a dozen. This persisted for several decades.
Over the decades, as the Authority's Church grew in power, the cult was displaced east, and the ogre-mage with them. Hearing of the greath wealth of Yoon Suin, and of the Rajah of Syr Darya's generous contracts to skilled mercenaries, the ogre mages manipulated the cult into crossing the mountains of the Moon (they were not so high back then) and entered Yoon Suin.
Because of the curse of Syr Darya, the cult moved south and east, and is no longer as firmly controlled by the Ogre Mages. They are desperately trying to keep the knowledge of the potency of the god-brain away from the Slug-men. So far they have succeeded, but they know it is but a matter of time.
Flesh of the Abbatoir God:
These are several reputed, rumored or speculated magical items that can be created from the flesh of the Abbatoir God. The following are mostly confirmed:
Divine sausage: Not only do these sausage fill the eater with divine strenght (treat as potion of fire giant strenght) they also have minor healing properties (heal 1d6 hp).
Hide of the god: Leather from the Abbatoir God is well suited for enchantment. That from a chosen one of dwarven background makes for particularly potent armor (+2 CON on top of other effects).
Bristles of the god: the coarse hair of the Abbatoir God is useful for brushes used to scribe magical scrolls with divine spells. Ground in a powder, they can be used to make dust of sneezing and choking.
Headcheese of the God: As detailed above, elevates the mind to a higher plane and provides magic. A very well kept secret. A potion made with cerebral fluid will grant the drinker an extra MD (1 use only).
Eyes of the God: No known properties, but the Ogre-Mages, as a diversionary tactic, keep spreading rumors that they are phenomenal. Sooner or later someone will find the way to use them properly.
The priests of the Vulture God are very curious about the Abbatoir God's flesh, but leery of consuming it or offering it as sacrifice. What if they - or their God! - is chosen?
For each template of Ogre Mage, your HP goes up by 2 and your strength and intelligence goes up by 1 each. You gain one Spell Dice (SD) and learn spells (see table below)
A: Large fame, +1 SD
B: Ogre weapon, +1 SD
C: Fast healing, +1 SD
D: Tough, +1 SD
Large frame: You gain +1d6 HP. You are 7 feet + 1d6 inches tall, and you grow another 6 inches per template.
Ogre weapon: Your weapon damage dice goes up by one step. An ogre dagger does 1d8 dmg, etc.
Fast healing: You heal 1d6 hp per hour of rest.
Tough: You reduce incoming damage by 1.
Spells: Roll a 1d6 at level 1, 2 and 3 to learn 1 spell (reroll if the same spell is obtained). At level 4, choose 1 spell and roll a 1d8 for another.
3: Polymorphe to humanoid form
4: Ogrify - inflict the Ogre Curse on a cruel child.
5: Charm person
7: Gaseous form
8: Cone of Cold
Finally, the Abattoir God should not be confused with Rustok the God of Butchers. Takes the form of a blood-stained grey langur (a type of monkey), favored color is yellow, bones are his preferred sacrificed. The God himself is never sacrificed, oh no, and this whole abattoir "God" is heretical nonsense.
Edit: some more writings on the Abattoir God (and other very neat cults), by a group of authors, can be found here.