Devour Essence

You begin to emanate a shadowy aura that appears almost otherworldly. For the duration your harmful spells begin to take back some expended power from each target slain by your hand. All of your damaging spells and abilities gain an additional 1D8 necrotic damage, additionally, whenever your spell deals the killing blow to a creature while you still concentrate on this spell, you may refund, one expended spell slot of 3rd level or lower for each creature slain.

When you cast this spell using a spell slot of 4th level or higher, increase the damage by 1D8 per spell level, also increase the level of spell slot that can be refunded by 1 per spell level.