Way of the Dark Soul

Monks of the Way of the Dark soul Rely on careful planning and constant persistence. They will always return from death, but everytime they come back they lose part of their humanity (or dragonborninity or gnomeinity ect.).  They are lethal against single targets and hard to pin down and attack.

Consult your DM on how their undeath will reflect in the campaign. You can portray them as being one more death away from going insane or completely losing their humanity so that there is still a consequence to death.

Do a Barrel Roll

Once you take this option at level three, you gain the ability to maneuver your way out of attacks and spells. Whenever you are attacked, as a reaction you can impose disadvantage on the attack by rolling out of the way. You can use this feature a number of times equal to your dexterity modifier. You regain all uses of this feature when you finish a long rest.

You also gain advantage on dexterity saving throws against spells and traps as long as you can see the source.

Lastly, you gain proficiency in acrobatics if you don't already have it.

Back Stab

Starting at level 6, you can attempt to attack an enemy in a vulnerable spot.

Whenever you attack an enemy with a melee weapon, you can make an acrobatics check with the target's AC being the acrobatics DC. On a success, your attack automatically hits and counts as a crit. If your acrobatics check is less than the target's AC however, you fail the attack and leave yourself open. While open, attacks against you will automatically hit until the end of your next turn. 

Mastery Of Death

Beginning at 11th level, you use your familiarity with death to escape its grasp. When you are reduced to 0 hit points, you can expend 1 ki point (no action required) to have 1 hit point instead.

The Dark Soul

Starting at level 18, you choose one of the following benefits:

Embrace the Abyss

You gain blindsight out to 10 feet. You constantly swallow light that surrounds you. No light, magical or otherwise can exist within 10 feet of you. This 10 foot circle counts as a magical darkness. You count as heavily obscured and attacks against you have disadvantage unless they have a means to see through magical darkness. Your Do a Barrel Roll feature will now let you avoid attacks entirely instead of imposing disadvantage. You may have your attacks deal necrotic damage whenever you like.

Embrace the Fire

You gain immunity to to fire and radiant damage. In addition to this, you also constantly put off a blinding light within 10 feet of you. Any enemies within 10 feet of you are considered blinded until they leave the 10 foot radius. You can use this as a distraction. Whenever you use your Back Stab feature, you have advantage on the acrobatics check. You may have your attacks deal radiant damage whenever you want.

Embrace the Insanity

You choose to embrace the insanity. Your Mastery of Death feature no longer costs Ki. Instead, every time you use the feature, roll a D20. On a 1 or a 20, you roll a D4. On a one or two, roll on the short term madness table. On a three or four, roll on the long term madness table. In addition to this, if you ever die, you will revive at the nearest town or safe haven 24 hours later. The only way to permanently defeat you is to imprison you.