Anathema

A yuan-ti abomination’s quest for godhood might lead it to perform a ritual that, if successful, transforms it into an even greater form: a yuan-ti anathema. This ritual demands the sacrifice of hundreds of snakes and requires the abomination to bathe in the blood of its enemies. The transformation is quick yet painful. Not all yuan-ti are eager to see one of their own become an anathema, since anathemas brutally subjugate their lessers for their own evil ends.

Not Quite Divine. 

An anathema considers itself a demigod on the path to greater divinity. It demands obeisance from weaker yuan-ti and uses every resource at its disposal to launch small-scale wars against its neighbors. Each conquest brings new slaves and sacrifices, as well as glory and riches, that the anathema thinks it needs to achieve true divinity.
An anathema’s most loyal yuan-ti followers see it as the pinnacle of the serpentine form, an unbelievable improvement on the nearly perfect abomination. Its devoted human followers think of it as “divine flesh in a mortal body,” and cultists serving an anathema tend to be more bloodthirsty and self-sacrificing in its presence.

Immortal. 

Anathemas don’t age, allowing them to pursue their goals until the end of days. Truly powerful ones can grow to rule multiple yuan-ti cities and bring entire regions, including humanoid realms, under yuan-ti control.