Mage Killer
Mystra and her followers are anathema to those that follow the true goddess of magic, Shar.
Those most blessed are chosen when their blood born skills become apparent to the Sharran priests, and the young sorcerers are taken into the temple to be taught the correct view of the world.
As they grow and develop their sorcerous powers within the safety of the temples they are indoctrinated into a loathing of the mystra view of magic and those that hold it. As the sorcerers grow stronger they are taught combat skills to complement their use of Shar's gifts creating a melange of martial and magical power focused with one purpose... to eliminate Mystra's church and ultimately facilitate the ascendance of Shar as the true goddess of all magic.
Basically the idea is to create a range (probably for stealth and tracking) that uses the sharran sorc abilities to hunt and kill mages.
They will abhor the casters of mystras weave, and seek to eliminate them where possible, interfere with any plans they know of, etc etc
Selunites could be similarly targetted as Shar/Selune are also antagonistic.
Mechanically i would suggest Sorc4/ranger x to allow 2nd level spells to boost damage and give thematic appearances, ranger provides some stealth, skill points and tracking, and full Ab.
potentially shadow dancer or assasin prcs could be suitable eventually depending on development.