Way of the fighter's fists

This monastic tradition was created and mastered by adventures. Many of the users who use this style of fighting are brawlers who trained in becoming as powerfull as possible with as little help from weapons and armor as possible. This style of fighting is seen often in arena fights or by thugs. The original tradition was crafted by a barbarian who sought to calm themself down, but for him to still be able to puch his foes into oblivion when neccesary. 

Bullet punch technique

You have trained at lot. When reaching level 3, you have finally mastered the art of the bullet punch technique, named for the speed of which you will be attacking your enemies on the battlefield. When making an unarmed attack as an action, you can make a second unarmed attack as a reaction as long as it is against the same enemy who you have attacked with the previous punch. When you get the extra attack feature at level 5, you can make two unarmed attacks per reaction following the same rules using this ability. 

Fists of steel

Due to the intense training regimen you have been following, your fists have hardened to a point where they are stronger than flesh and bone could ever be. Because of this, the damage you deal with all unarmed attacks (be it from a regular unarmed strike, an unarmed strike form the Martial Arts feature or the pullet punch technique) are increased by half your proficiency modifier rounded down. And what's more, you have learned to take advantage of a foe to hit them even harder. When you deal damage with any unarmed strike if you are attacking an enemy on which you have advantage on the attack roll, instead of half your proficiency, you can add your full proficiency modifier to the damage done by that attack. 

Critting blows

Critting blows is obtained at level 11. Thanks to your practical experience gained from fighting, you are now able to target your enemy's weak spots automaticly when fighting. This means that when you roll a 19 or 20 on any unarmed strike attack roll, you make a critical hit. Due to your ability to take advantage of your foes, this number is lowered to 18 when having advantage on an attack roll with a unarmed strike. This means that when having advantage on any unarmed strike attack roll, the number you need to roll for a critical hit becomes 18, 19 or 20.

Hands of the Grim Reaper's embrace

At 17th level, you gain the power to decide your opponent's fate. You have unlocked the gift from the Grim Reaper himself. You can spend your action, bonus action and reaction to make one death punch.

This death punch deals 14d10 bludgeoning damage and counts as an unarmed strike. This damage cannot be ruduced in any way. After seeing the amount of damage done, you can chose to spend ki points to raise the damage. With each ki-point spend, you add 2 necrotic damage to the total amount. Each ki-point also adds a +1 to your attack roll for the death punch. Make an attack roll the same way you'd make one for an unarmed strike to see if the attack roll hits. When you hit and the targets still lives afterwards, it must make a constitution saving throw. The DC is 8 + your DEX , CON or STR modifier (whichever is higher) + your proficiency modifier + each ki-point spend on the death punch. If the target fails, it will be stunned and fall prone. If the target succeeds, it will only fall prone.

When using this feature, you take 2 levels of exhaustion in the process and take as much necrotic damage as ki-points spend on the death punch.