Monks of the Way of the Monster follow a taboo tradition that utilizes mimicry and alteration to one's sense of self. These monks learn to channel the power of their bodies to become more than what was thought possible, changing their selves to the more ferocious and monstrous aspect of the world. This practice requires that students maintain their sense of self as they change their bodies by their force of will into dangerous and even disgusting forms.

Monstrous Strikes

Starting when you choose this tradition at 3rd level, you can augment your mode of attack such as growing crooked claws or hardened nails. You can choose to convert the normal bludgeoning damage of your Unarmed Strikes into slashing or piercing damage.

Monstrous Manifestations

At 3rd level, you gain the ability to manipulate your body into monstrous manifestations. You gain two monstrous manifestations of your choice at 3rd level, 2 more choices at 6th level, 2 more choices at 11th level, and 1 more choice at 17th level. Your choices are limited on what level the option is available at 3rd, 6th, and 11th level. Additionally, after a long rest, you can choose of the manifestations you know and replace it with another manifestation that you could learn at that level.

(3rd-level options)

Amphibious. You can breathe air and water. Additionally, you gain a swimming speed equal to your walking speed.

Keen Hearing and Smell. Tapping into bestial senses, you have advantage on Wisdom (Perception) checks that rely on hearing or smell.

Ignited Illumination. Your skin glows as though your blood was fire. As a bonus action, you can set yourself ablaze harmlessly or extinguish your flames. While ablaze, you shed bright light in a 10-foot radius and dim light for an additional 10 feet.

Manticore’s Tail Spike. You manifest a tail with numerous spikes. You can make a ranged attack (range 100/300 feet) with it dealing 1d4 + your Dexterity modifier piercing damage. This natural weapon is affected by your Martial Arts feature.

Hag's Mimicry. You can mimic animal sounds and humanoid voices. A creature that hears the sounds can tell they are imitations with a successful Wisdom (Insight) check against your Ki save DC.

Shadow Stealth. You attune yourself to the incorporeal aspects of monsters. While in dim light or darkness, you can take the Hide action as a bonus action.

Blood Drain. While grappling an opponent, you can attach to it with blood sucking mandibles manifested on your body or hands. So instead, at the start of each of your turns, the target loses 1d4 + your Wisdom modifier in hit points due to blood loss, and you heal the same amount.

Gargoyle's Skin. While you remain motionless, you are indistinguishable from an inanimate statue. Additionally, you have advantage on Dexterity (Stealth) checks to hide in rocky terrain.

Temporary Resistance. To learn to manifest innate defenses of monsters. As a bonus action, you may expend 1 ki point and choose one damage type to gain resistance to for the next hour until you choose a different one with the feature replacing the previous one.

Wakeful. When you're asleep, you manifest another head of yourself that is always awake.

(6th-level options)

Amorphous. Understanding the ooze means to meditate on the concept of the body without form. You can move through a space as narrow as 1 foot wide without squeezing. Any equipment you are wearing or carrying is transformed and merges into your form.

Burrowing Creature. You manifest hardened claws and body allowing you to strike the earth with speed. You gain a burrowing speed equal to your walking speed and gain tremorsense up to a distance of 60 feet.

Spider Walker. You harness the spirit of the spider granting you a climbing speed equal to your walking speed. Additionally, you ignore movement restrictions caused by webbing. Furthermore, as an action, you can spend 2 ki points to cast web.

Devil's Sight. You can see normally in darkness, both magical and nonmagical, to a distance of 60 feet.

Hurl Flame. You prove capable to manifest infernal flames allowing to make a ranged spell attack to a distance of 150 feet dealing 3d6 + your Wisdom modifier in fire damage. If the target is a flammable object that isn't being worn or carried, it also catches fire. Whenever you take the Attack action on your turn, you can use Hurl Flame in place of one of those attacks.

Limited Telepathy. You can magically transmit simple messages and images to any creature within 120 feet of it that can understand a language. This form of telepathy doesn't allow the receiving creature to telepathically respond.

Shapechanger. You learn the power of the innate manipulator that many demons or aberrations possess. You can use your action to polymorph into a Small or Medium humanoid, or back into your true form. Other than its size and speed, your statistics are the same in each form. Any equipment you are wearing or carrying isn't transformed. You reverts to your true form if you die.

Troll Regeneration. You manifest the regenerative properties of troll's blood. You can expend 1 ki point to regain 5 hits points at the start of your turn. If you take acid or fire damage, this feature can't be used at the start of your next turn.

(11th-level options)

Ethereal Jaunt. You can become capable to make brief jumps into the world beyond just as other creatures do. As a bonus action, you can expend 2 ki points to magically shift from the Material Plane to the Ethereal Plane, or vice versa.

Manifested Wings. You may sprout wings from your back in any form you like such as angelic wings or overgrown bat wings. As a bonus action, you may expend 2 ki points to gain a flying speed equal to your walking speed for 1 hour.

Intoxicating Touch. You can channel the enchantments often employed by monsters seeking to weaken their enemy. Whenever you take the Attack action on your turn, you can expend 2 ki points and use Intoxicating Touch in place of one of those attacks. The target is magically cursed for 1 hour. Until the curse ends, the target has disadvantage on Intelligence, Wisdom, or Charisma saving throws and all ability checks.

Barbed Hide. At the start of each of your turns, you deal 1d10 piercing damage to any creature you are grappling you, or vice versa.

Rusting Touch. You now utilize the properties of monsters capable of destroying ferrous metals. You may corrode a nonmagical ferrous metal object that you touch it, this also applies when you attack with your Unarmed Strikes. If the object isn't being worn or carried, the touch destroys a 1-foot cube of it. If the object is being worn or carried by a creature, the creature can make a Dexterity saving throw (8 + your proficiency bonus + your Dexterity modifier) to avoid your touch.

If you touch either metal armor or a metal shield being worn or carried,  you may give it a permanent and cumulative −1 penalty to the AC it offers. Armor reduced to an AC of 10 or a shield that drops to a +0 bonus is destroyed.

You may corrode any nonmagical weapon made of metal that hits you. After dealing damage, the weapon takes a permanent and cumulative −1 penalty to damage rolls. If its penalty drops to −5, the weapon is destroyed. You may destroy nonmagical ammunition made of metal that hits you after it does damage.

Spores. You manifest the toxicity readily apparent in many monsters. As an action, you can expend 3 ki points to emit a 15­-foot­-radius cloud of toxic spores extends out from you. The spores spread around corners. Each creature in that area must succeed on a Constitution saving throw against your Ki save DC or become poisoned. While poisoned in this way, a target takes 1d10 poison damage at the start of each of its turns. A target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. Emptying a vial of holy water on the target also ends the effect on it.

Amorphous

Understanding the ooze means to meditate on the concept of the body without form. You can move through a space as narrow as 1 foot wide without squeezing. Any equipment you are wearing or carrying is transformed and merges into your form.

Amphibious

You can breathe air and water. Additionally, you gain a swimming speed equal to your walking speed.

Barbed Hide

At the start of each of your turns, you deal 1d10 piercing damage to any creature you are grappling you, or vice versa.

Blood Drain

While grappling an opponent, you can attach to it with blood sucking mandibles manifested on your body or hands. So instead, at the start of each of your turns, the target loses 1d4 + your Wisdom modifier in hit points due to blood loss, and you heal the same amount.

Burrowing Creature

You manifest hardened claws and body allowing you to strike the earth with speed. You gain a burrowing speed equal to your walking speed and gain tremorsense up to a distance of 60 feet.

Devil's Sight

You can see normally in darkness, both magical and nonmagical, to a distance of 60 feet.

Ethereal Jaunt

You can become capable to make brief jumps into the world beyond just as other creatures do. As a bonus action, you can expend 2 ki points to magically shift from the Material Plane to the Ethereal Plane, or vice versa.

Gargoyle's Skin

While you remain motionless, you are indistinguishable from an inanimate statue. Additionally, you have advantage on Dexterity (Stealth) checks to hide in rocky terrain.

Hag's Mimicry

You can mimic animal sounds and humanoid voices. A creature that hears the sounds can tell they are imitations with a successful Wisdom (Insight) check against your Ki save DC.

Hurl Flame

You prove capable to manifest infernal flames allowing to make a ranged spell attack to a distance of 150 feet dealing 3d6 + your Wisdom modifier in fire damage. If the target is a flammable object that isn't being worn or carried, it also catches fire. Whenever you take the Attack action on your turn, you can use Hurl Flame in place of one of those attacks.

Ignited Illumination

Your skin glows as though your blood was fire. As a bonus action, you can set yourself ablaze harmlessly or extinguish your flames. While ablaze, you shed bright light in a 10-foot radius and dim light for an additional 10 feet.

Intoxicating Touch

You can channel the enchantments often employed by monsters seeking to weaken their enemy. Whenever you take the Attack action on your turn, you can expend 2 ki points and use Intoxicating Touch in place of one of those attacks. The target is magically cursed for 1 hour. Until the curse ends, the target has disadvantage on Intelligence, Wisdom, or Charisma saving throws and all ability checks.

Keen Hearing and Smell

Tapping into bestial senses, you have advantage on Wisdom (Perception) checks that rely on hearing or smell.

Limited Telepathy

You can magically transmit simple messages and images to any creature within 120 feet of it that can understand a language. This form of telepathy doesn't allow the receiving creature to telepathically respond.

Manifested Wings

You may sprout wings from your back in any form you like such as angelic wings or overgrown bat wings. As a bonus action, you may expend 2 ki points to gain a flying speed equal to your walking speed for 1 hour.

Manticores' Tail Spike

You manifest a tail with numerous spikes. You can make a ranged attack (range 100/300 feet) with it dealing 1d4 + your Dexterity modifier piercing damage. This natural weapon is affected by your Martial Arts feature.

Rusting Touch

You now utilize the properties of monsters capable of destroying ferrous metals. You may corrode a nonmagical ferrous metal object that you touch it, this also applies when you attack with your Unarmed Strikes. If the object isn't being worn or carried, the touch destroys a 1-foot cube of it. If the object is being worn or carried by a creature, the creature can make a Dexterity saving throw (8 + your proficiency bonus + your Dexterity modifier) to avoid your touch.

If you touch either metal armor or a metal shield being worn or carried,  you may give it a permanent and cumulative −1 penalty to the AC it offers. Armor reduced to an AC of 10 or a shield that drops to a +0 bonus is destroyed.

You may corrode any nonmagical weapon made of metal that hits you. After dealing damage, the weapon takes a permanent and cumulative −1 penalty to damage rolls. If its penalty drops to −5, the weapon is destroyed. You may destroy nonmagical ammunition made of metal that hits you after it does damage.

Shadow Stealth

You attune yourself to the incorporeal aspects of monsters. While in dim light or darkness, you can take the Hide action as a bonus action.

Shapechanger

You learn the power of the innate manipulator that many demons or aberrations possess. You can use your action to polymorph into a Small or Medium humanoid, or back into your true form. Other than its size and speed, your statistics are the same in each form. Any equipment you are wearing or carrying isn't transformed. You reverts to your true form if you die.

Spider Walker

You harness the spirit of the spider granting you a climbing speed equal to your walking speed. Additionally, you ignore movement restrictions caused by webbing. Furthermore, as an action, you can spend 2 ki points to cast web.

Spores

You manifest the toxicity readily apparent in many monsters. As an action, you can expend 3 ki points to emit a 15­-foot­-radius cloud of toxic spores extends out from you. The spores spread around corners. Each creature in that area must succeed on a Constitution saving throw against your Ki save DC or become poisoned. While poisoned in this way, a target takes 1d10 poison damage at the start of each of its turns. A target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. Emptying a vial of holy water on the target also ends the effect on it.

Temporary Resistance

To learn to manifest innate defenses of monsters. As a bonus action, you may expend 1 ki point and choose one damage type to gain resistance to for the next hour until you choose a different one with the feature replacing the previous one.

Troll Regeneration

You manifest the regenerative properties of troll's blood. You can expend 1 ki point to regain 5 hits points at the start of your turn. If you take acid or fire damage, this feature can't be used at the start of your next turn.

Wakeful

When you're asleep, you manifest another head of yourself that is always awake.

Pack Tactics

At 6th level, you have advantage on an attack roll against a creature if at least one of your allies is within 5 feet of the creature and the ally isn't incapacitated.

Monstrous Charge

At 11th level, you become empowered by the spiritual strength and power of many monsters. If you move at least 20 feet straight toward a target and then hit it with a attack on the same turn, the target takes an extra 2d8 damage of the attack's damage type. If the target is a creature, it must succeed on a Strength saving throw against your Ki save DC or be knocked prone.

Monsterification Master Art

At 17th level, you have mastered your tradition of mimicking monster abilities, proving yourself capable to imbue yourself with the powers of the strongest monsters. You may choose only of the following options.

Damage Absorption. As an action, you may choose a damage type so that whenever you are subjected to that damage type, you take no damage and instead regain a number of hit points equal to the damage dealt. This damage absorption lasts for 1 hour, and you can’t create it again until you finish a long rest, unless you expend 4 ki points to create it again.

Draconic Breath. As an action, you exhale with draconic energy in a 35-foot cone. Choose a damage type: acid, cold, fire, lightning, or poison. Each creature of your choice in that area must make a Dexterity saving throw against your Ki save DC, taking 8d10 damage of the chosen type on a failed save, or half as much damage on a successful one. You can’t do this again until you finish a long rest, unless you expend 4 ki points to do it again.

Hydra Heads. You may produce multiple serpent heads from your body granting you advantage on saving throws against being blinded, charmed, deafened, frightened, stunned, and knocked unconscious. Additionally, using these serpent heads when you take the Attack action on your turn, you may instead attack with the Hydra Heads dealing piercing damage that have a reach of 10 feet that are considered to be Unarmed Strikes for the purpose of benefitting from other features.

Damage Absorption

As an action, you may choose a damage type so that whenever you are subjected to that damage type, you take no damage and instead regain a number of hit points equal to the damage dealt. This damage absorption lasts for 1 hour, and you can’t create it again until you finish a long rest, unless you expend 4 ki points to create it again.

Draconic Breath

As an action, you exhale with draconic energy in a 35-foot cone. Choose a damage type: acid, cold, fire, lightning, or poison. Each creature of your choice in that area must make a Dexterity saving throw against your Ki save DC, taking 8d10 damage of the chosen type on a failed save, or half as much damage on a successful one. You can’t do this again until you finish a long rest, unless you expend 4 ki points to do it again.

Hydra Heads

You may produce multiple serpent heads from your body granting you advantage on saving throws against being blinded, charmed, deafened, frightened, stunned, and knocked unconscious. Additionally, using these serpent heads when you take the Attack action on your turn, you may instead attack with the Hydra Heads dealing piercing damage that have a reach of 10 feet that are considered to be Unarmed Strikes for the purpose of benefitting from other features.