This arrow is a magic weapon powered by the sacrifice of your own life energy and explodes upon impact. If you hit a creature with this arrow, you can spend one or more Hit Dice, up to your maximum Hit Dice. For each Hit Die spent in this way, you roll the die and add your Constitution modifier to it. You lose hit points equal to the total, and each creature within 10 feet of the target, including the target, must make a DC 15 Dexterity saving throw, taking necrotic damage equal to the hit points you lost on a failed save, or half as much damage on a successful one. You can't use this feature of the arrow if you don't have blood. Hit Dice spent on this arrow's feature can't be used to regain hit points during a short rest. You regain spent Hit Dice as normal.