Blood drain

A streak of blood flashes from your pointing finger to a point you choose within range and then blossoms into a pool of blood that explode. Each creature in a 20-foot-radius sphere centered on that point must make a Dexterity saving throw. A target takes 8d6 necrotic damage on a failed save, or half as much damage on a successful one.

The target must have an (artifact, potion) that gives necrotic resistance to resist it. (it works on undead)  

You gain half the damage as temporary hit points, for 1 min or the end of your next round.

There will be a bloody mess after... 

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d6 for each slot level above 3rd.