You are an assassin that has been sworn to secrecy by the Paragons Call. You have spent a lifetime training for the moments when you are called upon to sneakily end a life. 

Critical Damage Dealer

You gain access to 2 crit dies which are d8s. When you hit with a melee attack you can expend a crit die to add a d8 to the damage. The d8 rolled from the crit die is always a critical hit (meaning you double damage only from the crit die). If you were to roll a 20 on your attack this then becomes a double crit (meaning you triple the damage only from the crit die).

You gain an additional crit die at levels 9,13, and 17.

Assassins Creed

You are proficient in a forgery kit, poisoners kit, and disguise kit. You also gain proficiency in deception and survival skills. You have advantage on stealth checks while in combat.

Stealth Assassinations

If you are hidden you gain advantage on an attack roll and if you roll a 20 on an attack roll you can roll a d8 to determine how much true damage you deliver to your opponent.

1-4: Normal Crit Damage

5,6,7: Double Crit Damage (3 times)

8: if the enemy has less than 100 HP it dies instantly

You also now have the ability to take the hide action as a reaction after your turn.

True Assassin

You have mastered the way of the hidden assassin. You now crit on 17-20. This crit applies to all damages including crit dies.

Assassins in the Making

You can spend 1d4 days training a sidekick assassin. When in combat it takes its initiative after you. On its turn it uses the dodge, hide, or help action. If it is close to an enemy that moves into or out of its combat zone it can take a reaction to get an attack of opportunity. As a bonus action you can have the sidekick attack using the assassin stat block. When your sidekick attacks it is always a critical hit. You can expend 2 crit dies to make this a double critical (3 tines damage). Attacks of opportunity are not critical.

Assassins Initiative

Your so adept to combat that now in the first round you can make 2 turns. The first turn is on your initiative that rolled and the second turn is your initiative-10. You can only use this feature twice per short rest.