Mage Slayer

 
Prerequisite(s): Spellcraft 2+ ranks, Base Attack Bonus 3+
 
Benefit: You gain a +1 to Will saves, spell casters that you threaten cannot cast defensively, and are aware of this fact. if you are a spellcaster and take this feat, your caster level is reduced by 4 for all spells and spell-like abilities.
 
Source: Complete Arcane, Miniatures Handbook