Mage Burr(Complete Scoundrel, p. 100)
Level: Bard 1, Hexblade 1, Sorcerer 1, Wizard 1, Spellthief 1,
Components: V, S,
Casting Time: 1 standard action
Range: Close (25 ft. + 5 ft./2 levels)
Target: One creature wearing armor or using a shield
Duration: 1 round/level (D)
Saving Throw: Fortitude negates
Spell Resistance: Yes
Sharp ridges, split leather, and cracking patches of rust spread over your enemy's armor like an angry, irritating disease.
Jagged edges and rough surfaces break forth all over the target creature's armor and shield. These protrusions deal no damage and are little more than an uncomfortable annoyance. Arcane spellcasters, however, find the effect most distracting, incurring double the normal arcane spell failure chance for armor and shields. In addition, any creature affected by this spell takes a -5 penalty on Concentration. checks. The check penalty does not worsen if an affected creature is both wearing armor and using a shield.
For example, a wizard wearing chainmail and carrying a light steel shield would normally have a 35% chance of arcane spell failure. That wizard, if targeted by this spell, would incur a 70% chance of arcane spell failure, as well as taking a -5 penalty on Concentration checks.
This spell has no effect on unarmored opponents or on creatures with only natural armor or an AC bonus from items other than armor.