Slumbering dragon ring, lingering dragon and along with hidden body spell is very effective when fighting these enemies.
The best projectile magic I use and/or recommend is Great Deep Soul or Deep Soul due to its fast cast and low FB cost.
While invisible, cast either one of the orbs until the foe goes down. Be sure to have the daughter of chaos staff (cannot spell it's true name) due to its dark aliment.
Cation - Don't get too close, keep a great distance at all times or else they will figure where you are and your cover will be blown until you or it dies.
Great Heavy Soul arrow is also great but the time to cast it is too long in my opinion. If you have a maxed out Court Sorcerers staff then happy hunting! You will one shot them each time.