You give of your flesh in order to call forth a dark creature of great power.
Benefit: When you cast a summon monster spell, you may declare that you are making a bargain. If you do, you may choose to summon any evil outsider from a summon monster list up to one spell level higher than you can normally cast. The creature is summoned inside your actual body and emerges in a welter of blood, dealing 1d8 damage per HD of the summoned creature to you. Other than than this restriction, the creature acts as if summoned normally.
A freakish and dramatic feat that can give you a surprise advantage in a fight. If allowed, a GM should take note when a player takes this feat, as it can allow them to make certain dramatic encounters easier. Fortunately, the high cost of the feat means they probably won’t be using it all day!