Hidden Blade

You have mastered the art of the unseen strike. Whether you act in crowds of people, social gatherings or bump into an unlucky victim at the docks. Nobody is safe from your fast knives and deadly daggers, without being any the wiser of whom caused them misfortune or death. Not only have you honed your public shanking capabilities, you also learned to make use of your environment to enhance your stealth skills.

Fighting Style

You learn the Two Weapon Fighting Style. If you already know the Two Weapon Fighting Style, instead chose one from Archery or Defense.

Hiding in Plain Sight

When you choose this archetype at 3rd level you gain the ability to hide in places you never thought possible. You gain advantage on stealth checks in crowds and you can attempt to hide when you have ½ cover. When you hit a surprised target with a weapon attack, you can make a Dexterity (Stealth) check with disadvantage to stay undetected (panic breaks out but it was not obvious that you were the culprit of the attack). If you pass this check, you can not use this feature again until you finish a long rest.

Swift Strikes

Starting at 5th evel, when you make a weapon attack with a melee weapon you are proficient in that has the light or thrown property, you can make a second attack with your off-hand melee weapon as long as you are proficient with it and it has the light or thrown property.

Stabbing Expertise

Starting at 9th level, you can add twice your Proficiency Bonus to damage rolls when you hit with a melee weapon that has the light or thrown properties. 

If you make a successful attack with a dagger at 9 level  you deal 1d4 (weapon Die) +8 (twice your Proficiency Bonus)+ your Dexterity Modifier as piercing damage.

Flying Daggers

Also starting at 9th level you have mastered to art of thrown weapons. This allows you to ignore 1/2 and 3/4 cover when you make ranged attacks with thrown weapons and doubles your effective range with thorwn weapons. 

Additionally, half your proficiency modifier rounded down times per day as an action, you can cast the Cloud of Daggers spell without expending a spell slot. At 15 level you upcast the spell as a 3rd level spell.

Deadly Sneak Attack

By 13th level you can apply sneak attack twice per round as long as both attacks meet the requirements for sneak attack. You can use this feature equal to your proficiency bonus -2 times per day. The second time you apply sneak attack you can add a number of d6 equal to your proficiency bonus -2 to the damage.

At 13th level you would deal 7d6 sneak attack damage on the first and 3d6 sneak attack damage on the second attack

Cloak and Dagger

Also at 13th level, if you wield a dagger in your main or off hand and also wear a cloak, add +1 to your Armor Class

Unseen Strikes

When you reach 17th level, you have become the master of attacking without being seen. Your strikes with melee weapons with the light or thrown properties have become to fast to see with the naked eye. When you make an attack roll with a melee weapon with the light or thrown properties you get advantage and +2 to hit. Additionally attacking with a melee weapon with the light or thrown property no longer ends invisibility effects that normally would end when you take the attack action.