Spell Vulnerability

(Spell Compendium, page 200, DnD 3.5)

Transmutation

Level: ; Cleric 4; Sorcerer/Wizard 3
Components: V, S
Casting Time: 1 round
Range: Close (25 ft. + 5 ft./2 levels)
Target: One creature
Duration: 1 minute/level
Saving Throw: Fortitude negates
Spell Resistance: No

A violet spray springs from your fingertips and wraps around your opponent. It fades into a dull purple glow, which attracts spell energies as opposed to shrugging them off.

This spell reduces the subject's spell resistance by 1 per caster level (maximum reduction 15). This reduction can't lower a subject's spell resistance below 0.