Way of Death and Kombat

Inspired by Shang Tsung from Mortal Kombat, this build is to bring a Soul Stealing Warlock feel to a martial artist without having to Multiclass into Warlock. The idea is that the life essence that you steal from people can be fused with your Ki to create necromantic and evocation(preferably fire)spells. Eventually you will have drained so much essence that you can summon visions or faces from the lives you've stolen and can use their lives to save you in a pinch. 

Soul Expense

Starting when you choose this tradition at 3rd level, you gain the ability to cast warlock spells. Wisdom is your spellcasting ability for your warlock spells, so you use your Wisdom whenever a spell refers to your spellcasting ability. In addition, you use your Wisdom modifier when setting the saving throw DC for a warlock spell you cast and when making an attack roll with one. You gain 1 cantrip and 3 spells off the warlock spell list but you can only choose either evocation or necromancy spells off the list. You gain an additional spell every 3 levels of monk and additional cantrips at 5th and 12th LVL, still only choosing from the 2 schools of magic.  At LVL 3 you have access to 1st LVL spells, then at 6th 2nd LVL spells, at 9th 3rd LVL, at 13th 4th LVL, 17th 5th LVL. For every 1st LVL spell the cost to cast is 2 Ki points, at higher levels the Ki point cost goes up 2 for every LVL of the spell.  Additionally, when you gain a level in this class, you can choose one of the warlock spells you know and replace it with another spell from the warlock spell list, which also must be of a level for which you have access to.

Soul Drain

At 3rd level, your study of death allows you to extract the Life essence from another creature as it nears its demise. When you reduce a creature within 5 feet of you to 0 hit points, you gain temporary hit points equal to your Wisdom modifier + half your monk level rounded up(minimum of 1 temporary hit point).

Soul Invocation

You gain a invocation from a select list off of the original Warlock invocation list. At 6th LVL you can choose 1 invocation from the following list: Agonizing blast(WIS Modifier), Beguiling Influence, Fiendish Vigor, Grasp of Hadar, Lance of Lethargy, Mask of Many Faces, Misty Visions, or Repelling Blast. At 9th level you gain another Invocation along with adding to the list of available invocations from the following: Sculptor of Flesh, Minions of Chaos, and Whispers of the Grave. At 17th level you gain a 3rd invocation and adding to the List with the following: Master of Myriad Forms and Witch Sight. When u gain a level in this class you can change out a invocation for another on the appropriate list according to your class level. 

Mastery of Death

Beginning at 11th level, you use the life essence you have to save yourself from death in a moment of need. When you are reduced to 0 hit points, you can expend 1 ki point (no action required) to have 1 hit point instead.

Touch of the Long Death

Starting at 17th level, your touch can channel the energy of death into a creature. As an action, you touch one creature within 5 feet of you, and you expend 1 to 10 ki points. The target must make a Constitution saving throw, and it takes 2d10 necrotic damage per ki point spent on a failed save, or half as much damage on a successful one.