This isn't a threadcrap, I promise, but I think yuan-ti are cool.
I like the idea that there's a hierarchy of snakemen from the most humanlike purebloods at the bottom of the pyramid - deliberate metaphor, oh yes! - who infiltrate human society establishing cults and corrupting the unwary, through the snake-headed halfbloods who would, one presumes, be the serious agents and soldiers guarding temples and the like, right up to the much more snakelike abominations who are the prophets and warlords of the race.
Still, you can use pretty much any similarly-structured hierarchy of evil creatures to stand in for them. Knowing nothing about The Shattered Gates of Slaughtergarde, why not find a devil of the appropriate CR? It can be an emissary of Tiamat, or something.