Blood Expulsion

You draw sacrifice some of your own vitality, taking 1d6 necrotic damage, and draw the blood from every creature in a 30-foot cube centered on a point you choose within range. Each creature in that area must make a Constitution saving throw. Constructs, plants, elementals and some undead aren't affected by this. A creature takes 5d8 necrotic damage on a failed save, or half as much damage on a successful one. 

For each enemy killed by this spell, you gain 1d8 hit points.