Avada Kedavra

The caster forms a glowing green bolt of energy that lances toward a targeted creature. On a hit, the target gets a dexterity saving throw, if passed the creature takes 1d6 Necrotic damage. If failed, the creature suffers instant death. A Critical Hit with Avada Kedavra cancels the saving throw and the target dies. However, if it's cast preemptively, on a Hit, the Protago Ultimus spell negates the instant death effect, but brings the target to Zero Hit Points. Protago Ultimus does not neutralize the 1d6 Necrotic damage.