Pathfinder: Blood Magic

Blood magic is the use of a spellcaster's own life force to power his magic. Casters normally draw power from external forces: the primal essence of nature, a god or saint, the leylines of arcane energy, and others besides. But another source exists - the caster himself. Using one's own life energy to power a spell is dangerous and costly, but when a mage is desperate, it can prove necessary.

How To Use Blood Magic
Blood magic does not necessarily involve spilling blood, though in a ritual setting, many spellcasters choose to do so as a symbolic gesture. The real drain is imposed by the spell, which draws power directly from the mage.

When a spellcaster chooses to use blood magic, he must voluntarily sacrifice hit points: 25%, 50%, 75%, or 100% of his maximum hit points. This can be done regardless of the caster's current hit points; a caster with only 1 hit point remaining could choose to sacrifice 100% of his maximum hit points. He would, however, become unconscious immediately after the spell was cast, and likely die as well. No effect short of divine intervention can prevent this damage.

For each 25% of maximum hit points sacrificed in this way, the spell gains +1 spell levels and +2 caster levels. The additional spell levels may be used to cast any spell that the caster had prepared during that day, or that the caster knows if he casts spontaneously. Additional spell levels may also be used to add metamagic feats to the spell. A spontaneous spellcaster does not take longer to cast a blood magic spell, even if the spell uses metamagic feats.

If a spellcaster chooses to sacrifice 100% of his maximum hit points, he gains additional benefits. The spell he casts may be any spell on his class list, so long as it is not from a banned school. If he chooses to apply metamagic feats to the spell, he may apply any metamagic feat, whether or not he has that feat.

Recovering From Blood Magic
Damage taken from blood magic must heal by natural recovery. No healing magic short of divine intervention can restore hit points lost to blood magic. The Heal skill can be used to speed recovery as normal, but magical healing is not possible.

Marks of Blood Magic
Sufficient use of blood magic can change a spellcaster's body. No organized research has been conducted due to the dangers inherent in blood magic, but some mages have found scars or odd markings on various parts of their body. The exact effects seems to vary from one individual to the next.