Corrupt Summons

Transmutation [Evil]
Level: Demonologist 3, Sor/Wiz 4
Components: V, S
Casting Time: 1 action
Range:Medium (100 ft. + 10 ft./level)
Area: 50-ft.-radius spread
Duration: 1 hour/level

The caster creates an area in which only evil creatures can be magically summoned. No matter what a later caster attempts to summon, he actually summons an evil version (a fiendish beast rather than a celestial one, for example) or an evil equivalent (a devil rather than a formian). If the summoner was attempting to summon a good or neutral creature, the evil creature that appears does not obey the commands of the summoner or attack his enemies. Instead, it attacks the summoner, and the spell that summoned the evil creature cannot be dismissed. A corrupt summons spell can be dispelled normally, however.