Reasons for Rework: Assassing has always felt to me like a front loaded class that doesnt really provide a lot of unique features in the later levels. In my perspective, the vanilla incarnation of the assassin has a lot of redundant abilities like Impostor and Infiltrator expert which are ultimately roleplay abilities. You do NOT need a class ability to grant you permission to disguse yourself or mimic someones voice, these are things that you can just DO. Besides, we both know that your GM is still going to make you roll for it, even if your sad excuse for an ability says you can do it unerringly. Which means that while your friends are out there trearing holes in reality and smiting arch devils all you got to show for your commitment to this class is a failed performance check and a one way ticket to the gallows. NO sir, I aim to remedy that with this juicy rework

As an assassin, you dedicate yourself to the art of death. To that end, you strive to master all manner of tools and techniques to kill whoever so happens to be your target. Those who adhere to this archetype are diverse: hired killers, spies, bounty hunters, and even specially anointed priests trained to exterminate the enemies of their deity. Stealth, poison, and disguise help you eliminate your foes with deadly efficiency. 

 

Tools of the Trade

You gain proficiency with one martial or simple weapon and one tool of your choice. You can change the proficiency granted by this feature to a new weapon or tool after spending a long rest studying and practicing its use. 

Assassinate

Starting at 3rd level, you are at your deadliest when you get the drop on your enemies. 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.

Silent Killer

You have become an expert at moving and striking silently. When you are hidden from a creature, they have disadvantages on any perception check made to find you. Additionally, when a surprise attack you make reduces a creature to zero hit points, you can immediately use your reaction to attempt to hide in one swift motion, you may also hide the dead body as a part of the same reaction if your target is a Medium or smaller creature. 

Escape Plan

You have honed your skills to become a lethal avatar of death, striking from the shadows and vanishing in an instant. As a bonus action, you can initiate an escape maneuver allowing you to Disengage, Dash and Hide as a part of the same action. Once you perform an escape you cant do so again until a new initiative is called. 

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.