Type: General
Source: Fiendish Codex I
You can draw upon the living essence of a willing or captured demon to fuel the creation of items or the casting of potent spells.
Prerequisite: Any two item creation feats, Demon Mastery.
Benefit: Whenever you need to expend experience points to craft a magic item or cast a spell with an XP component, you can draw upon the life force of a nearby demon to reduce the XP cost to you. Before beginning the process, you must secure a demon whose Hit Dice equal or exceed the caster level of the item or spell in question. The demon could be one that you summoned with a planar ally spell, or one that you have bound with a planar binding spell, or even one that you simply encountered and convinced to aid you. The demon need not be willing, but it must remain within 30 feet of you for the duration of your work on the item or the casting time of the spell, and you must have line of effect (but not necessarily line of sight) to it during that time.
Drawing essence from a demon does not increase the time required to craft the item or cast the spell, but the process is draining for both you and the demon. Each of you rakes 1d6 points of Constitution damage when the essence is channeled from the demon into your body, then converted into magical energy.
An unwilling demon can attempt a Fortitude save (DC 10 + 1/2 your character level + your Cha modifier) to resist removal of its essence. Success negates your use of this feat and forces you to either pay the full cost yourself or abort the creation or casting.
Successfully drawing essence from a demon in this way reduces the XP cost of the spell or item creation by one-half, but it complicates the process. If you use this feat to reduce the XP cost of a spell, you must succeed on a Concentration check (DC 20 + the demon's HD) to cast the spell. If you use this feat to offset the XP cost of crafting a magic item, the demon's essence has a 10% chance to corrupt the item in some way, imbuing it with a curse. (The DM determines the nature of this curse randomly by rolling on the tables on pages 272-273 of the Dungeon Master's Guide.)