You have chosen to follow a long forbidden art of assassination, utilizing the Taboo Shadow magic long locked away and hidden by the Kinkou Order. Those who adhere to this archetype have received training from a master in this art, usually due to a belief that the only sure way of protecting one's self and ones people is to obtain the power necessary to do so, and show no hesitation in using it to do so. Keeping to the shadows and using them both to attack and avoid being attacked, those who follow the Way of the Shadow are unmatched in their ability to take out a target quickly, and vanish into their surroundings. Your Archetype grants features at the 3rd level and then again at 9th, 13th, and 17th levels.

One with the Shadows

When you choose this archetype at 3rd level, you get 120ft darkvision and can attempt to hide when only lightly obscured.

Living Shadow

At 3rd Level you gain the ability to manifest a copy of yourself as a Living shadow at any location you can see within 15ft of you as a bonus action. This shadow is intangible, cannot be dispelled, destroyed, moved or attacked and is unaffected by magic-cancelling as it is not an inherently magical effect. This shadow will last for 18 seconds (3 rounds). You can swap places with your shadow once during its duration as a free action. Swapping places will not provoke opportunity attacks. Your shadow will attempt imitate the first Attack action you take on each of your turns against a target within it's range as if it were wielding the same weapon you are. Shadows cannot wield ranged weapons, or weapons which you do not have proficiency in, it may only wield melee and thrown weapons. Make separate attack and damage rolls for your shadow's attack.

Purge the Weakness

Starting at 9th level, you gain the ability to sense weakness and fear in your opponents. When an enemy is bloodied your sneak attacks become empowered, allowing you to roll d8's rather than d6's.

Shadow Step

At 13th level, you gain the ability to move through physical terrain such as walls, doors, horse carts, etc. Upon activating this ability you take on a shadowy form for 12 seconds (2 rounds) and become unaffected by terrain of any sort, be it difficult or normally impassable. In addition to this, your walking speed increases by 10ft for the duration. If you are inside of a solid object at the end of 12 seconds you will be shunted to the nearest open space and take 2d10 Force damage. 

Death Mark

Starting at 17th level, you become a master of instant death. You can use a Bonus Action to mark a creature within range for death. Upon doing this you vanish, leaving behind a Living Shadow in the location you were upon activating this feature. You may swap positions with this shadow once as a free action without provoking an opportunity attack. Your next attack automatically gains sneak attack bonus and all of your attacks against the target that hit are automatically critical hits. Note that the Living Shadow created by this feature will not dispel other Living Shadows, and will not be dispelled by using the Living Shadow feature, allowing you to have 2 living shadows active.