Dirty Magical Shot

Your level of dirty ranged fighting has extended to the realm of spellcasting. Whenever an opponent has his back turned to you, you know how to manipulate the magic in your arrow to target his weak point, doing severe amounts of damage.

Prerequisite(s): 8th-level Arcane Archer

Benefit: This feat works exactly the same way as the Dirty Shot feat, except that spell arrows that attack an enemy from behind do double the normal amount of damage.