Choose a creature within range that you can see that is a humanoid and has blood of some form (DM's Interpretation). Upon doing this, they then must make a Constitution saving throw, on a failure taking 3d10 necrotic damage as you tear a small hole on a major artery, causing blood to seep from the wound, or half as much on a successful one. You then draw the blood to yourself and quickly refill one of your blood vials with the same amount of hit points that the creature lost. The creature additionally will lose 1 maximum hit point every round until they stop the bleeding in some way.