Perfect Summons

Transmutation [Good]
Level: Sorcerer/wizard 4
Components: V, S
Casting Time: 1 standard action
Range: Medium (100 ft. + 10 ft./level)
Area: 40-ft.-radius spread
Duration: 1 hour/level
Saving Throw: None
Spell Resistance: No

You create an area in which only good creatures can be magically summoned. No matter what a later caster attempts to summon, he actually summons a good version (a celestial beast rather than a fiendish one, for example) or a good equivalent (an archon rather than a formian). If the summoner was attempting to summon a neutral or evil creature, the good creature that appears is not bound to obey the commands of the summoner or attack his enemies. Instead, it deals with the summoner as it sees fit—possibly attacking an evil caster. The summoning spell cannot be dismissed, though it can be dispelled. A perfect summons spell can also be dispelled normally.

Perfect summons counters and dispels corrupt summons, and vice versa.