For quite a while I've been intrigued by the thought of Shadovar and the way that they worship Shar and, overall, how different Shar's clergy is within the Shadovar as opposed to about everywhere else outside of the plane of shadow. Unfortunately all we seem to be given about Shadovar religion is Shar and there's a temple called the Fane of Shar. It feels a little to bare for a culture openly dominated by a clergy usually kept under wraps. It would be great to get a discussion going so other shadovar (especially other clerics) can have some ideas for their stories. A lot of this is basically my own head-canon to fill in blanks so bear with me.
I see it running sort of like a mix of the medieval Roman Catholic church and the Bene Gesserit from Dune with shadovar clerics of shar being seen as a cultural essential thanks to Shar's influence on them but of slightly less status in a magocracy, openly welcomed yet seen with suspicion as they're known to spy for the greater clergy and the Princes. The Fane itself is a massive cathedral, one of the most grand structures to Shar built by mortals, that holds regular ceremonies and sermons (which there are MUCH more of than the Prime churches), enforcing regular worship from most of the nobility and all of the commoners on pain of excommunication/exile, possibly more violent punishments depending on crime and status. Both high and low born shadovar can find a way to an influential life through the church, though rigorous tests of devotion to Shar are placed upon lower born and any trying to rise beyond a certain rank.
The church sees the Plane of Shadow as Shar's holy realm and see themselves as Shar's chosen. They're prone to automatically assume they have an authority over Sharran's on the Prime because of this, and that their small and secretive churches are but parts of the true church. This authoritative pride does not translate in to ignorance on Shar's reputation on the prime, and most clerics would still act with caution where it's due.
Now smaller details I can leave up to imagination but I'd really love to hear some other thoughts on this.