The Monk of the Way of the Spirits is one who has mastered their inner spiritual animal, the beast manifesting as a tattoo upon their back. Many of these practitioners are more so travelling warrior-sages than actual monks, though the art originates from Oni monasteries. The spirits of their souls assist them in battle in many ways, bringing death and destruction upon their opponents. These animals take form of ghostly creatures circling around their masters, and the tattoo on their back gains in detail as they master the art more and more. 

Level 3: Spiritual Fire

At 3rd level, you have begun your path down the ways of the spirit, nurturing your spiritual animal, your fists can blaze with ghostly fire. Whenever you make an unarmed attack, you can choose to deal fire damage instead of bludgeoning. The damage die remains the same as the martial arts' die.

Spiritual Battle Aura

Also At 3rd level, you have learned to harness your inner magics and turn your battle aura into a deadly weapon.
The outline of a magical tatto of a creature representing your soul appears on your back. The creature can be a dragon, tiger , kirin or scorpion. You may only have one spirit animal, and may not change it midway through your journey down the way of the spirits.
Using your bonus action, you may expend 2 ki points to release your rage into a visible aura of ghostly flame around you, turning your eyes and the outline of the tattoo glowing.
While you aren't wearing armour in this form, you gain the following benefits:
-Advantage on Dexterity checks and saving throws
-Additional 15 feet of movement speed
As well as an additional benefit depending on your tattoo:
-Dragon: While using your Spiritual Battle Aura, you become resistant to bludgeoning, slashing and piercing damage while in your Spiritual Battle Aura.
-Tiger: Your hands manifest the spectral claws of a Tiger, which add a +2 to your attacks' damage. This increases to a +3 at level 6, and +4 at level 11.
-Kirin: While using your Spiritual Battle Aura, you can make ranged unarmed strikes that deal lightning damage equivalent to your damage die. This attack has a range of 30 feet and uses wisdom as it's attack and damage modifier. 
-Scorpion: Your body is empowered by the durable carapace of the scorpion. Your AC increases by 1 at level 3, 2 at level 6 and 3 at level 11.

This aura lasts for 1 minute, unless you are knocked unconscious, or end your turn having not attacked an enemy and not taken damage since the end of your last turn. At the end of the aura's normal duration, you may expend a 2 ki points without using any actions to extend it's duration for another minute. You cannot do this if the aura ends prematurely for aforementioned reasons.

 

Spiritual Strike

At level 6, you have become capable of summoning the spirit of your beast to battle along your side to make a deathly strike. The manner of this strike depends on your spirit. As an action you can expend 3 ki points to make the following strike:
-Dragon: Your dragon spirit makes a deathly lunge from beyond, making an attack against a single target within 30 feet of you, dealing slashing damage equivalent to 3 times your current damage die.(For example if your damage die is a D8, it deals 3D8 Damage)
-Tiger: Your tiger spirit manifests through your claws, allowing you to cleave through targets in front of you in a 15 foot cone, dealing damage equivalent to 2 times your damage die
-Kirin: Your kirin spirit manifests in your body, allowing you to make a strike empowered by lightning, making a single strike which deals lightning damage equivalent to 2 times your current damage die, in addition to your basic bludgeoning or fire damage
-Scorpion: Your scorpion spirit manifests in your body, through a ghostly sting, allowing you to use your reaction instead of action in order to make a powerful counterattack after an enemy misses an attack against you. This attack deals piercing damage equivalent to 4 times your current damage die.
Additionally, at all times you can use a bonus action to expend 1 ki point and bellow a piercing shout across the field of battle, which causes hostile creatures within 30 feet of you to have advantage on attacks against you and disadvantage on attacks against your allies.

One With The Spirits

At level 11, you have become harmonized with your spiritual animal, allowing you to gain the following benefits:
-Dragon:  While using your Spiritual Battle Aura, you manifest the image of a terrifying dragon. Any time you make 3 or more attacks against the same target in one turn, they have to succeed on a Wisdom saving throw(DC 8 + your dexterity modifier). On a failure, the target creature takes psychic damage equivalent to your martial arts die and is frightened for the next three rounds. A frightened creature may attempt a save at the start of each of it's turns to end the condition prematurely.
-Tiger: While using your Spiritual Battle Aura, your body manifests spectral claws, making all of your attacks hit in a 5 foot cone in front of you(The space you are attacking and two spaces on the side of that space). You can choose to make your attacks deal slashing damage instead of bludgeoning.
-Kirin: While using your Spiritual Battle Aura, your body is empowered by the speed and lightning of a Kirin, which allows you to make an additional attack as part of your attack action.
-Scorpion: While using your Spiritual Battle Aura, your Zone of Control is treated as if you had ten feet of reach. If an enemy moves, while within ten feet of you, you can, as a reaction expend 1 ki point, move five feet towards them and then make an attack of opportunity. You can choose to make your attacks deal piercing damage instead of bludgeoning.

Call of the Spirit

At level 17, you have become capable of calling forth your spirit to enter an empowered form of the Aura of Destruction, once per long rest. In this state, you gain the following benefits:
-You have advantage on Dexterity checks and saving throws
-You gain resistance to all bludgeoning, piercing and slashing damage as well as fire damage.
-Your unarmed damage dice increase to the next tier of martial arts die. (If you have a D4, it increases to D6, D6 to D8, etc. If you have a D12 damage die, it instead changes into 2D6).
-You have advantage on all checks against the following conditions: Blinded, Charmed, Deafened, Frightened, Paralyzed, Petrified, Restrained and Stunned

You also gain the following benefits depending on your spirit animal:

Dragon:
-Any time you make 3 or more attacks against the same target in one turn, they have to succeed on a Wisdom saving throw(DC 8 + your dexterity modifier) or be Frightened of you for the next three turns. A frightened creature may attempt a save at the start of each of it's turns to end the condition prematurely.
-All of your critical attacks cause the target to make a wisdom save or become frightened(DC=8+wisdom modifier)
-You gain immunity to bludgeoning, piercing, slashing and fire damage instead of resistance

Tiger:
-You are able to overcome resistance to bludgeoning, slashing and fire damage, and treat immunities to those damage types as if they were resistances when making an unarmed strike or using one of this subclass's features.
-Your attacks crit on 19s and 20s.
-You gain a +5 to your attacks' damage
-All of your attacks hit in a 5 foot cone in front of you(The space you are attacking and two spaces on the side of that space). You can choose to make your attacks deal slashing damage instead of bludgeoning.
Kirin:
-You are able to overcome resistance to lightning damage, and treat immunity to that damage type as if it was resistance when making using one of this' subclass's features
-You are able to make one extra attack as part of your attack action
-You can replace the damage you deal in your regular attacks with lightning damage
-You gain the ability to make a ranged unarmed strike against a target up to 30 feet away, so long as you are dealing lightning damage. The attack roll for this attack uses your wisdom modifier.

Scorpion:
-You are able to make two reactions per round
-Your counterattacks and attacks of opportunity are made at advantage and crit on 19s and 20s. 
-You gain an additional +4 to your AC

Your Spiritual Form lasts for one minute, unless you are knocked unconscious, or end your turn having not attacked an enemy and not taken damage since the end of your last turn. At the end of the aura's normal duration, you may expend five ki points without using any actions to extend it's duration for another minute. You cannot do this if the aura ends prematurely for aforementioned reasons.