Way of the Fiendish Heart

Monks of the Way of the Fiendish Heart channel the unholy energy of a powerful demon or devil residing within them. They teach that proper training and careful meditation can subjugate such a creature and harness its power to unleash fiendish attacks on their opponents.

Corrupted Soul

At 3rd level, your corrupted soul alters your body and imbues your unarmed strikes with the essence of a fiend. You gain the following benefits:

• Death Throes. If you become incapacitated or die, the fiendish power within you is unleashed in a fiery explosion. Instead of dropping to zero hit points, you drop to 1. In addition, each creature within 30 feet must make a Dexterity saving throw (the DC = 10 + your monk level), taking Xd6 fire damage (X = your proficiency bonus) on a failed save.  Once this feature is used, you can’t use it again until you finish a long rest.

• Fiendish Strike. When you damage a target with an unarmed strike, you can change the damage type to fire or lightning.

• Black Tongue. You learn to speak, read, and write Abyssal or Infernal (your choice).

Unholy Armaments

At 3rd level you can channel your ki to summon a fiendish weapon with which to punish your opponents. As a bonus action, you can spend 2 ki points to summon one of the weapons listed below.  You are proficient with it and it counts as a monk weapon for you. The weapon lasts for 10 minutes, after which it turns to ash and crumbles in your hand.  If you are incapacitated  or die, are disarmed, or otherwise drop the weapon, it immediately turns to ash and crumbles away. The weapons summoned in this way are manifestation of your ki and do not count as magical for the purposes of overcoming resistance and immunity to nonmagical attacks and damage.

• Balor's Blade. You summon a ghostly sword that crackles with lightning. The sword can take the shape of a shortsword, longsword, or scimitar (your choice).  It deals your Martial Arts die (+ your WIS modifier) slashing damage plus 1d4 lightning damage. If you score a critical hit with Balor's Blade, you roll for damage three times instead of twice.

• Balor's Whip. You summon a fiery whip. It deals 1d4 (+ your WIS modifier) slashing damage plus an additional amount of fire damage equal to your Martial Arts die. When you deal damage with this whip, you can spend ki points to increase the amount of fire damage dealt.  For every 1 ki point you spend, the fire damage increases by an additional Martial Arts die.

Profane Power

At 6th level, the fiend within you grants you the following:

• Magical Unholy Armaments. Attacks from weapons summoned using Unholy Armaments are considered magical for the purposes of overcoming resistance and immunity.

• Teleportation. When you use your Step of the Wind, you can spend an additional ki point to teleport, along with any equipment you are wearing or carrying, up to 30 feet to an unoccupied space you can see. You can use this feature a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

Fiendish Aura

At 11th level, the power of the fiend within now radiates from you, wreathing you in flame. As a bonus action, you can create an aura of fire that surrounds you for 1 minute. For the duration, you gain the following effects:

• Fiery Shield. You gain a +2 bonus to your AC. If you are hit with a melee attack, the attacking creature takes 1d6 + your WIS bonus in fire damage.

• Resistance. You gain resistance to fire, lightning, cold, and poison damage.

Black Heart

At 17th level, you are one with the fiend inside you; heart, mind, and soul. You gain the following benefits:

• Truesight. You gain truesight out to 10 feet.

• Telepathy. You gain Telepathy up to 120 feet.

• Explosive Aura. When you activate your Fiendish Aura, unholy fury explodes from you. Choose any number of creatures you can see within 30 feet. Each of those creatures must succeed on a Dexterity saving throw against your ki save DC or take 3d10 fire damage.