Blood Extraction

You conjure a pulsating red orb floating in the air at a point you can see within range. It lasts for the duration and gives off dim light for 20 feet. At the end of each of your turns until the spell ends, each creature other than you within 20 feet of the orb must make a Constitution saving throw. On a failed save, a creature takes 3d6 necrotic damage, or 3d12 necrotic damage if its hit points are less than or equal to half of its maximum hit points. On a successful save, a creature takes half damage. 

If a creature is reduced to 0 hit points by this spell, the orb collects some of its blood. It cannot collect blood from the same creature twice. When the spell ends, the accumulated blood strengthens you, instantly granting you 1d6 hit points for each creature the orb collected blood from. 

Using a Higher-Level Spell Slot. The damage increases by 1d6 and 1d12, respectively, for each spell slot level above 3.