Venomshank

As a rogue, you experimented with the paths you could choose to become more powerful. You thought you would be an assassin, but you found out that there was another path that suited you more: the path of poison...

Coated Blade

When you choose this archetype at 3rd level, you gain proficiency with the poisoner’s kit. Also, add poison damage equal to your dexterity modifier to your weapon attacks.

Critical Toxin

Starting at 3rd level, you are at your deadliest when you get the drop on your enemies. Any hit you score against a creature that is surprised is a critical hit, and if you score a critical hit with poison coating your blade then the poison does double damage.

Envenomed Blood

Starting at 9th level, you flood your body with deadly poison, as your body fights back and dilutes the poison, you magically replace your blood with that poison. Your blood is transformed into basic poison. As a result of this, you also gain immunity to poison damage.

Sleeping Gas

At 13th level, you gain the ability to blow a gas filled with a potent sleeping poison from your mouth in a 30 ft. sphere around you. This gas lasts for 5 minutes, and then disperses. Any creature affected by this must make a Constitution saving throw: on a failed throw they fall unconscious for the duration of the action, and on a successful throw nothing happens.

You may use this action a number of times equal to your proficiency bonus per long rest.

Poison Master

Starting at 17th level, you become a master of poisons and toxins. All poisons are doubly effective, and all  poison damage you deal is doubled.