Your fiendish pact enhances your magic while corrupting it with evil.
Prerequisites
Fiendish Pact, ability to cast 3rd-level arcane spells.
Benefit
You can use your Fiendish Pact to gain a +1 profane bonus to the save DC of any spell you cast. The spell gains the [Evil] descriptor.
If the spell targets a creature with the (Good) subtype, you gain a profane bonus equal to the number of Fiendish Feats you possess on any check to overcome its spell resistance.