The player can convert his vital essence (health) into magic, and that magic into spells. It's not a super useful spell though, as the drain rate is fixed, constant, and occupies a hand that could be casting magic or holding a weapon or shield. If somehow, the middleman of chain were to be cut out, it would be more effective.
I'm proposing a method of magic that uses both Health and Stamina as the reservoirs drained to cast spells: Blood Magic.
If you want to damage an enemy, you cast a Damage Health spell. To do 50 points of damage you need to spend say, 70 or so points of Health and Stamina combined. If there is no more Stamina, Health will be used in its place, but you cannot cast a spell if the cost will kill you.
The spell types would be varied, ranged, on touch, and stream effect, like current Destruction spells, along with other special effects, such as:
Tether: A stream of your blood ties an opponent close to you, unable to move a certain distance away at the risk of the player being unable to escape from said enemy.
Blood Rune: A rune placed on the ground or wall, once an opponent steps over or near it, it bursts outward doing damage, as well as temporarily bringing them to their knees from the effects.
Shield: A shield is conjured similar to a ward, but has the additional effect of being able to block attacks like a shield. You cannot cast or attack with this spell activated.
Blood Wraith: A wraith (red Ice Wraith) is summoned and attacks the opponent, draining their life and giving it to you along with biting attacks.
I think this would be a fun feature, and might allow warriors or a mage low on magic or high on health to make a risky but possibly worthwhile attack or defense. If you noticed, I tried to include effects along the lines of all the schools of magic, minus Enchanting for obvious reasons.
Tell me what you all think!