Trained in the art of killing magic users, Witch Hunters take great pleasure in ridding the world of them. Their arts simple: inflict so much pain they cannot cast spells.
Hatred of Mages
If a spellcaster is attempting to cast a spell while within your threatened range, you can take an attack of opportunity. This attack deals half damage and their spell automatically fails on a hit, or the spellcaster can elect to take full damage and their spell is only half as effective (deals half damage, half the penalty, etc.)
This replaces the Martial Talent gained at 1st level.