Blade of Blood

Your weapon becomes coated in blood, extending and sharpening its edge. Make a melee attack. On a hit, the target suffers the weapon attack’s normal effects, as well as taking your spellcasting modifier in Necrotic damage, and 1 Necrotic damage per HP you sacrifice to the attack, sacrificing a maximum number of HP equal to your wizard level, and a minimum equal to the damage per HP. If your attack kills the target, and they are not an Undead or Construct, this cantrip costs no damage.

At Higher Levels. At 5th level, each HP sacrificed is worth 2 necrotic damage. This increases to 3 at 11th level, and 4 at 17th level.