If the target fails the save, you may take 1d4 necrotic damage as you bleed yourself to increase the damage to 1d12. The damage you take can't be reduced in any way.
This spell doesn't affect creatures without blood in their bodies, such as undead or constructs.
This spell's damage increases by one die when you reach 5th level (2d8 or 2d12), 11th level (3d8 or 3d12), and 17th level (4d8 or 4d12).