Way of the Inner Spirit

A monk whose soul is composed of a deity, and draw on that deity's power to manifest their inner energy in the form of a ghastly presence. A monk can only adopt the Way of the Inner Spirit by sacrificing their own soul to serve as an avatar to a minor deity; upon death, this deity searches for a new potential avatar willing to accept them.

Level 3: Claws of the Inner Demon

As a bonus action, you can spend 1 KP to summon the claws of your inner demon. When you do so, each chosen creature you can see within 10 ft. of you must succeed on a Dexterity saving throw or take force dmg equal to two rolls of your Martial Arts die.

For 10 minutes, these ghastly arms extract from you. Their form depends on the appearance of the deity residing with you.

While the claws are present, you gain the following benefits:

• You can use your WIS in place of your STR (modifiers) while making STR checks/saving throws.

• When you make an unarmed strike with the claws on your turn, your reach is 5 ft. greater than normal.

• The unarmed strikes you make with the arms can use your WIS in place of your STR or DEX (modifiers) for the ATK/DMG rolls, and deal force dmg.

Level 6: True Face of the Inner Spirit

 As a bonus action (also while activating Claws of the Inner Demon), you can spend 1 KP to wear your True Face for 10 minutes, unless you are incapacitated or die.

While wearing the face, you gain the following benefits.

Demon Eyes. You gain 120 ft. of darkvision (for normal/magical darkness).

Spiritual Knowledge. You gain advantage on the following checks: WIS (Insight) and CHA (Intimidation).

Spirit's Tale. You can speak directly into the mind of a creature of your choice that you can see within 60 ft., or you can speak with a loud voice audible in a 600 ft radius around you.

Level 11: Wholeness of the Inner Demon

If both the claws and the true face are present, you can manifest the rest of the entity's body around your physical self (no action required). 

While the entity is present, you gain the following benefits.

Spectral Protection. If you are hit with thunder/lightning/fire/cold/acid/force damage, you can use your reaction to reduce the amount by 1d10 + your Wisdom modifier, or at least by 1.

Fury of the Claws. If you land a hit on the target with your claws, you can deal extra damage to it equal to your Martial Arts die.

Level 17: Inner Demon Possession

As a bonus action, you can spend 5 KP to summon the claws, true face, and form of your astral self and have it possess you for 10 minutes, ending early if you are incapacitated or die.

While possessed, you gain the following benefits.

Demonic Shell.  +2 bonus to Armor Class.

Storm of Claws. If Extra Attack feature is used, you can attack three times if all the attacks are made with your claws.