Rogue: Variant Assassin

You focus your training on the grim art of death. 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.

Bonus Proficiencies

When you choose this archetype at 3rd level, you gain proficiency with the Disguise Kit and the Poisoner's Kit if you don't already have it. Your proficiency bonus is doubled for any ability check you make that uses either of those proficiencies, if it is not already.
Disguises and poisons you make using these proficiencies take half the time and one-quarter of the resources to make.

Assassinate

You learn how to use more nimble weapons to strike where it really hurts. When using a light melee weapon, your Sneak Attack dice become d8s when you have advantage on the attack. Attacks without advantage or without a light melee weapon still deal normal Sneak Attack damage.
Additionally, you've also learned how to use simple poisons in the most deadly ways possible. You can use your Cunning Action to coat your weapon in Basic Poison, provided you have it on your person. When coated this way, the enemy automatically fails the Con Save, and the Poison deals 2d4 damage instead. This damage increases by 1d4 at 9th level (3d4), 13th level (4d4) and 17th level (5d4).

Infiltration Expertise

Starting at 9th level, you can unfailingly create false identities for yourself. You have advantage on all Disguise Kit and Charisma (Deception) checks you make in regards to making a new identity or keeping your cover. Additionally, if you spend five minutes listening to somebody speak, read their handwriting, or see their behavior, you can unerringly mimic their speech, writing or mannerisms. This ruse is indiscernible to the casual observer, but wary creatures suspecting something is amiss make a Wisdom (Insight) check versus your Charisma (Deception).
You also can use this time to learn how much people are worth. After observing someone for five minutes you can estimate what you would need to bribe someone, if they can be bribed at all. Bribes made in such a manner give advantage on any Charisma (Persuasion) checks made to convince someone to do something for you or allow you to do something.

Master Poisoner

At 13th level, you've learned more of the secret arts of poison. Poisons you create ignore poison resistance. Additionally, you've learned how to create a poison that burns the target from the inside out. When making a vial of Basic Poison, you may choose to have it deal Acid damage instead.
Your expertise with poison has also strengthened your body against their effects. You now have resistance to poison damage, and have immunity to the poisoned condition. If any other feature already gave you resistance to poison damage, you are now immune to it.

Death Strike

Starting at 17th level, you become a master of dealing death. During the first round of combat, you double the amount of Sneak Attack dice you roll.
Additionally, whenever you roll Sneak Attack, you may reroll a number of dice equal to your Dexterity modifier, and choose either result.