Shadow Blade

You balance the line between throwing knives and shadow work.  You can make the transition seamlessly.  Your ability to strike from the shadows is unmatched as well as your knife throwing capability. 

FLYING BLADES

You have been training with throwing knives your whole life you are more deadly at it and are quick to throw your additional ones.  At first level you are able to use proficiency bonus for the number of attacks while using throwing knives. IE: 1st level proficiency bonus is +2 therefore you get two attacks while using throwing knives and each knife does 1d6 damage.   9th level proficiency bonus is +4 therefore you get four attacks while using throwing knives and each knife does 1d8 damage. See chart below.

Level 1- Two attacks 1d6 each knife thrown.

Level 5- Three attacks 1d6 each knife thrown.

Level 9- Four attacks 1d8 each knife thrown.

Level 13- five attacks 1d8 each knife thrown.

Level 17- Six attacks 1d8 each knife thrown.

ASSASSIN'S MARK

Starting at first level you have the ability to hone in on your target.  You choose a creature you can see within range and mark it as your target. You deal an extra 1d6 damage to the target whenever you hit it with a weapon attack.  You can use this ability as many times as your proficiency bonus modifier. You regain this ability after a long rest. For example at 6th level your proficiency bonus is +3 so you may use the ability 3 times in a long rest cycle. 

Shadow Strike

From the shadows you make an attack with your throwing knifes. Starting at 3rd level, you have advantage on attack rolls against any creature that hasn’t taken a turn in the combat yet. In addition, any hit you score against a creature that is surprised is a critical hit.

Shadow Walker

At 9th level, you gain the ability to step from one shadow into another. When you are in dim light or darkness, as a bonus action you can teleport up to 60 feet to an unoccupied space you can see that is also in dim light or darkness. You then have advantage on the first melee attack you make before the end of the turn. 

Shadow Weapon

At level 13, you may bond your throwing knifes to yourself, through a 1 hour long ritual. You can summon the throwing knifes at will from the shadows or dismiss it into them.  The throwing knifes bonded to yourself in this manner also deals 1d6 necrotic damage to a target on a hit.

Death Strike

Starting at 17th level, you become a master of instant death. When you attack and hit a creature that is surprised, it must make a Constitution saving throw (DC 8 + your Dexterity modifier + your proficiency bonus). On a failed save, double the damage of your attack against the creature.