Knowing the things you know has caused you to lose all hope. You have focused your entire existence on hiding in the dark and ending the life of others because deep down you know that the life you have is an undeserved one. In a world filled with magic and wonder you have no need for any of it. You have cast off such trival things because the only thing in life that is certain is death. You can and will do anything to get the kill, no matter if it is a king, a warrior, or a peasant. They all fall to your blade the same. You have become death and with it you are the only thing that is certain. 

Slaughter

You have grown so accustomed to killing you do so fluidly without thought. When you surprise attack or flank attack an enemy with a weapon attack, you may use your remaining movement to close in and make another weapon attack to a different enemy within range. You have advantage on the attack and can apply your sneak attack to this next attack as well. You can only use this feature once per turn.

One Step Ahead

You are always one step ahead and quick to take down unsuspecting victims. For you the first strike is the most important as it sets the flow and tone of combat. You gain a bonus to initiative and gain advantage against and deal increased damage to enemies who haven't taken a turn in combat yet. If you kill an enemy before they get a turn in combat, you keep the increased damage for 2 more additional rounds for every attack you make. The damage is 3D10 and is the same type of your weapon. 

Murderous Retaliation

When an enemy has the courage to actually strike you, you immediately return the favor and leave them regretting their decision. You use your reaction to attack an enemy within range who just damaged you in a vital organ or part of their body where the armor is exposed. You have advantage on the attack and if you hit they must make a constitution saving throw DC 8 + your dexterity modifier + your proficiency bonus. If they fail the saving throw they have disadvantage on any and all attacks (including spells) until the end of their next turn. This feature can only be used twice per long rest. 

Feign Death

You are willing to take the lowest road possible to reach your goal. When you are down but not quite yet out, you no longer rely on your hands to do the killing but your mind as well. If an attack reduces you to 25 or fewer hit points you may use your reaction to roll a deception check vs the enemy's perception or investigation check. If you succeed the enemy believes you to be dead. If you fail on your deception roll, the enemy gets a free attack on you with advantage.  On your next turn if you attack the enemy you deceived you have advantage and any and all hits you land on them will be critical strikes. You may only use this feature once per long rest.