In my current campaign?
Real, real far behind the scenes, they come in two flavors:
Children of the Outer Gods - all subtle in their own way, all psionic. Illithids (variant; think pseudo-Dark City Strangers), Aboleth, Yuan-ti, Kuo-toa, Tsocharr, etc. Real Lovecraftian type Far Realms aberrations, for the most part.
Cultists of the Devourer - Unbeknownst to just about everyone, the god Malar isn't actually who he seems. Malar is actually an Outer God known as the Devourer. The Devourer currently lies bound sleeping in an extradimentional prison, locked away by a particular druidic order from ages past. The dreams of the Devourer are what formed the facade of the god Malar and are what grant his adherants their spells. The Devourer has one purpose - when the time is right, to rise up and consume all life on Faerun (after which he'll leave, find another world, settle in until the flock is ripe and then repeat the process; it's kinda what he does). Most... 99.999n%, say.. of Malar's worshipers don't know a single thing about the true nature of their god. Of those that do, there's a big split: on one side, there are those who want to find the Devourer's prison and release their lord ASAP; and on the other there are those who say not to, it'll happen when it happens, and if you wake him up early he'll be pissed. So essentially, Bad Guy Apocalypse Cultists of Malar and Bad Guy Cultists of Malar Opposed to the Other Bad Guys.