Death of the Endless

Through your successful but still young career as an assassin, you have caught the attention of Death, arguably the most powerful of the Endless.
Perhaps you are very particular in the nature of your contracts and only choose ones of a certain alignment, or maybe you assassinated an extremely high profile target.

You have received a blessing from Death; the nature of which has expanded your power and connected you to the void, allowing you to channel it through yourself. She has gifted you with her sigil: an Ankh representing life which will allow you to focus your power, making you capable of removing the souls of those around you and banishing them to the Void, and stealing the life force from your enemies for yourself

Decaying Blades

Starting 3rd level, your blessing from Death allows you to draw power in order to create and wield shards of Void.

You do not need to have a weapon equipped in order to attack as if you were holding a dagger.
You can make a melee or ranged weapon attack with a dagger that deals necrotic damage; you can use this feature with two-weapon fighting.

You deal an additional die of damage against undead enemies with these daggers.

You gain additional attacks with these Void Daggers at 9th and 17th level; your sneak attack uses all of these attacks as your action.

Come And Go As You Please

"I will be the last thing in existence, and I will lock the door to the universe behind me"

Starting 3rd level, your gift from Death grants you the ability to control locks in order to travel freely, and do so without a trace.
You can cast Knock and Arcane Lock once each per short rest;

Additionally, 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.

Oh What Could Have Been

Starting 9th level, you gain the ability to view the future and attempt to find out when and how a target is destined to die; you can show the target, inspiring fear in their heart. When you end this person's life you steal the potential energy of their life force, empowering yourself.

You can spend an action to make a target that you can see roll a CHA save; on a failed save, you learn when and how they will die. The target can choose to fail this save and you can choose to have the target also see what you see.
If you show the target how they die, they become frightened until the end of your next turn. You are the source of their fear unless what they were destined to be killed by is within their sight.
If you reduce them to 0 hit points, you can steal the potential energy of their remaining life: you gain HP equal to your Rogue level, any excess HP is gained as temporary HP.

You can use this feature a number of times equal to your proficiency bonus and you regain these when you short rest.

It Is Your Time

Starting 13th level, you can reach into the souls of those you deem deserving, steal it from their bodies and banish it to the Void.

When you use your Sneak Attack feature with a melee weapon and your attack hits, instead of attacking the target you can choose to focus your power through your Ankh and attempt to banish the target's soul.
The target rolls a Death save; if their HP is higher than yours then they roll this save with advantage, if the opposite is true then they roll with disadvantage.
On a failed save then they are reduced to 0 hit points and their soul is banished, they cannot be revived and cannot regain HP.
On a successful save the target falls unconscious for 2 minutes, or until the end of your next turn in combat, you also steal health from the target equal to your Proficiency Bonus.

If you have seen how the target is destined to die, they receive a -5 modifier to their save, you steal their remaining HP when you banish them and their body crumbles to ash, or you steal double your proficiency bonus as HP from them on a save.

You can use this feature once per long rest and you gain an additional use at 17th level. 

One With The Void

Starting 17th level, you are able to wield the Void with more precision.

When you use your Decaying Blades feature to attack after stepping between shadows, all attacks you make with your action have advantage.

Additionally, the advantage is now applied if you make a ranged attack with the Void Shards as it is with melee attacks