Well, for FB's stunlock you basically need inserting Infernal stigma every 2-3 skills.
A good combo is: Stigma (12-18) - Completer ( don't know level ) - G.M. ( don't know level )
Try experimenting a bit with levels. They should be 9 or 12 for both GM and comp. and try 12-15-18 for stigma and see which works for you. And you can try adding abbysal crystal for its DPS.