Avada Kedavra

You utter the words "Avada Kedavra" which compels a creature you can see to die instantly. A willing creature within 5 ft of the target can use its reaction to make a DC 17 Dexterity check in an attempt to move in front of the original target and take all effects of the spell. The original target then becomes immune to all damage and other spell effects cast by you. This spell imposes 5 levels of exhaustion on you after 1d12 hours, and each long rest taken within 5 days decreases your level of exhaustion by 1. If all the long rests aren't taken within 7 days, the remaining levels of exhaustion never disappear.  Additionally, if you have not dedicated at least 10 years to studying this spell, your hit points and your hit point maximum decrease by 6d10 instantly, and you are transformed into an undead. If such an event occurs, your size decreases by 1, you can't level up in any class, and you can't cast spells higher than level 3.