A tiefling attempts to take the life of a lord, being stopped by the lord's two bodyguards, he makes short work of them, dodging out of the way of their attacks, he strikes both of them jugular, ending their lives swiftly.  The tiefling whirls around the form of the noble, snapping his neck before he could even get a breath out, and has already escaped by the time the lord's corpse has hit the floor. 

Mortal Blow

When you pick this monastic tradition at 3rd level you gain the ability to channel your own life force into your punches. When you hit an opponent with your unarmed strike, you can turn the hit into a Mortal Blow and add bonus damage up to your monk level to that punch; however, this bonus damage you add, comes from your own HP, you take damage equivalent to the bonus damage you deal using this ability. If you kill a target with this ability, you get the health you spent on the attack back.

Tormenting Connection

At 6th level, you gain the ability to share the damage you’ve taken with your opponents around you. As a reaction, you spend a Ki point and attack an enemy within your range and have them make a Constitution saving throw with DC equivalent to 8 + your wisdom modifier + your proficiency bonus. Upon failing said saving throw, they take damage equivalent to the damage you’ve taken throughout the round, and take half of that damage on a success.

Sacrificial Strike

At 11th level, you gain the ability to make your opponents fall unconscious by hitting them. When you make a Mortal Blow unarmed strike at your opponent, and the added damage would put you to zero health or lower, your opponent falls unconscious too. When you fall unconscious, you choose whether you’re stable with 1 HP, or unstable with 0, whichever you choose applies to your opponent as well.

The Death Punch

Your mastery of life force has given you the ability to get your opponent to death’s door in a single hit. At 17th level, whenever you make a Mortal Blow at maximum bonus damage, you can Spend 5 additional Ki ponts to kill your opponent instantly, when you use this feature, you cannot attack again until your next turn. You do not get your health refund from Mortal Blow when you use this ability.