Type: Reserve
Source: Complete Mage
With a touch, your magic corrupts the spells of your enemy.
Prerequisite: Ability to cast 5th-level spells.
Benefit: As long as you have an abjuration spell of 5th level or higher available to cast, you can make another creature's spellcasting harmful to itself. Use of this feat requires a melee touch attack that does not provoke attacks of opportunity. As a standard action, with a successful touch you can infuse another creature with baneful magic for a number of rounds equal to the level of the highest-level abjuration spell you have available. A successful Will save reduces this duration to 1 round.
For the duration of the effect, each time the target completes the casting of a spell, it takes damage equal to the level of the abjuration spell that determined the effect's duration. Since the spell's casting has already been completed, this doesn't count as damage dealt during casting.
As a secondary benefit, you gain a +1 competence bonus to your caster level when casting abjuration spells.