Monks on the Path of the Souls Shadow learn to manipulate the shadows around themselves and move unseen to allow them to move through and observe their surroundings from the shadows. learning to strike when required at the most opportune moments. 

A monk following this path is destined to write new scriptures and keep records of events through the observation of the world while remaining in the shadows. As time has passed, they realised that from the shadows they saw the corruption of those in power and swore to undermine them by eliminating their links to the criminal underworld where appropriate.
With the understanding that power above such as the kings and lords or emperors of the kingdom often find their way to the top through the use of the criminal underworld.

You channel your Ki points from the depths of your shadow, and manipulating it to your will. If you run out of Ki you have no shadow at all and cast no shadow on the ground until rested. but this can leave you at a disadvantage. any stealth checks made while you have no shadow are rolled at a disadvantage. 

Thanks and credit to the following for assistance with reworking this Monk SubClass.
AtlaStar, Wolfbat

Shade Script

In training to become a member of this tradition, you’ve learned a secret form of communication known only to other members of the Souls Shadow. These messages are inscribed into the very essence of shadow, and are only visible to members of the tradition. Due to the nature of the communication, the messages are symbols used to convey specific information, and are typically used to mark a target for assassination.
When you take this tradition at 3rd level, you learn to imprint symbols that convey a message of no greater than 10 words into any shadow you can see. The shadow itself holds the symbol, which moves with the shadow. You may only have one such symbol in place at a time, and using this ability again will destroy any symbols previously made. Creatures with truesight can see these symbols, but not convey their meaning unless they know the secret language of the Souls Shadow.

One with Darkness

The martial arts involved in manipulating shadows to bend to one’s whim is taxing on most that try, but through dedication and practice you have begun to learn how to not only control the shadow around you, but how to also avoid the obstructive nature of darkness itself.
Starting when you choose this tradition at 3rd level, you may spend a ki point to use a bonus action to hide while in dim light or darkness. The obstruction provided by the shadows are enough to hide in situations where you would normally be seen. In addition you can spend 2 ki points to duplicate the effects of the following spells.

Darkness
Darkvision

Penumbral Strikes

At 6th level, your dedication to the nature of shadow has allowed you to give them physical form. When you make a melee attack on your turn, your flurry of blows grants you 3 attacks, instead of two, as the coalesced shadows strike at your target in tandem with your attacks. If this attack is made while in darkness, it doesn't require you to spend ki points. In addition, when you use the stunning strike ability,  you may choose to instead inflict the blindness condition until the end of your next turn as the nearby shadows infuse with your ki, forcing its way into the targets eyes. 

Shadow Step

 

When you are in dim light or darkness, you can use a bonus action to hide. When you attempt to hide in an area obscured by dim light or darkness, you may do so even if a creature is able to see you. While hidden, leaving an area obscured in this way doesn't reveal your position until the end of your turn.

Manipulate Shadows

Through this tradition you’ve learned to manifest shadows in such a way as to make them more corporeal, giving them form beyond the simple mirrored strikes that your own shadow casts.

Beginning at 11th level, as an action you can spend 2 ki points to cause any area of darkness that you can see to become difficult terrain until the end of your next turn. In addition any number of creatures that you can see that end their turn in darkness take 1d8 + your wisdom modifier force damage

Protection of Shadows

Through training and tradition as you reach the 11th level in this path, you may as an action spend 3 ki points and summon the shadows surrounding up to 5 allies to protect them from a single critical hit. As you do so the shadows coalesce around the players and will soften the blow of the next critical hit and the protective shadows are then dispersed from all protected players.

Umbral Praetor

At 17th level, you’ve mastered the essence of shadow to become it’s master. As an action you can spend 2 ki points to summon a shadow warrior to assist you in combat.  This shadow warrior shares your ability scores, proficiency bonus, base movement speed, and has hit points equal to 3 monk hit die. Extending from it is a wispy darkness, forcing any light within in a 5 foot radius of the warrior to become dimmer. This turns bright light within range into dim light, and dim light into darkness.

As a bonus action on your turn you can mentally command your shadow warrior. Its attacks use your Martial Art’s damage die, dealing deal force damage. The shadow warrior can use any ability that you possess that requires ki. Ki spent this way is depleted from your own ki points.

You can summon this warrior a number of times per long rest equal to your Wisdom modifier (minimum 1)