You can power your magic with infernal energy, but this inflicts painful damage.
Prerequisites
Planar Bloodline (Demon or Devil) or Fiendish Pact.
Benefit
Once per day, you can take ability burn to cast a spell without losing the spell slot, and it remains prepared if you prepare spells. When using this ability, you take ability burn to each of your three physical ability scores (Strength, Dexterity, and Constitution) equal to the level of the spell cast + 1.
You may use this feat one additional time per day for every two Fiendish feats you possess.
You reduce the ability burn by 1 point for every three Fiendish feats you possess, to a minimum of half the spell’s level, rounded up.