Toxicant

The Noxious Rogue uses a poisoners kit to create Vials of Toxin and Vials of Venom. The Toxin Vials can be used to inflict select conditions on an opponent while the Vials of Venom deal poison damage upon impact. The Noxious Rogue gains features to bypass condition immunities and immunities to poison damage. Furthermore, this subclass gains access to a unique condition, Lingering Death, that deals poison damage at the start of the afflicted creature's turn when using the Vials of Venom. Lastly, a Noxious Rogue can gain sneak attack on all melee attacks while a creature is under the condition of either Vials.

Back Alley Alchemist

Starting at level 3, your knowledge of toxic materials allows you to create deadly substances.

You learn to create Toxin or Venom Vials using the poisoner’s kit. Creating either Vial requires 30 minutes of focused crafting and materials equal to 5GP in value. A total of 2/4/6 Vials can be held at a time at levels 3/6/9 respectively.

Vials created by Back Alley Alchemist have the following properties:

• All Vials have a DC of 10 + DEX + WIS/INT (chosen by the player). Targets that fail this CON Save suffer the effects of the Vial.
• Creatures that come into physical contact with the fluids within the Vial must make a CON save. The Vial is considered to be consumed if this occurs and the contents of the Vial will ignore any armor worn or non magical protection worn.
• If thrown the Vial acts as a improvised weapon with the Finesse property, but will deal no damage.
• The contents of a Vial can be poured onto a melee weapon as a bonus action or outside of combat. The next successful attack within 5 minutes will inflict the effects of the Vial if the target fails the CON save.
• Targets currently suffering from conditions applied by either Vials are immune to further conditions inflected by said Vials until the target has a successful CON save or the condition ends. 

The following Vials can be made using the poisoner's kit:

• Vial of Toxin - Upon creation designate a condition of either poisoned, stunned, blinded, or deafened. If the Vial succeeds, inflict the assigned condition to the target until the end of your next turn.
• Vial of Venom -  The venom within the vial will deal 1d6 + (1/2th Rogue Level rounded down)d6 poison damage up to a maximum of 5d6 poison damage.

Potent Poisons

At level 3, your understanding of toxicology allows you to exploit even the faintest of weaknesses.

Creatures that are usually immune to poison damage are now only considered to be resistant.

Furthermore, creatures that are immune to the conditions of your crafted Vial of Toxin are now affected said condition and must make a CON Save with Advantage. On a failed Save, they will suffer the effects of the condition.

Fatal Fumes

At level 9, your Vial of Venom will inflict the Lingering Death condition alongside dealing poison damage. The creature must make a CON save. On a failed save, the creature is afflicted with Lingering Death.

Lingering Death: At the start of the afflicted turn take damage equal to (1/2th Rogue who crafted the Vial of Venom Level rounded down)d6 poison damage up to 5d6 poison damage. The afflicted creature can attempt a CON save at the end of their turn. If they succeed, the condition ends. Otherwise, the condition persists until a minute has passed or the creature dies.

Viper Strikes

At level 13, you learn to abuse the numbed senses.

While a creature is under the condition given by one of your crafted Vials, all melee attacks by you are considered to be sneak attacks.

Practiced Medicine

At level 17th your familiarity with deadly poisons have made you an efficient apothecary even when unprepared. 

As a bonus action create a Vial of your choice instantly with no GP cost. This feature can be used twice per long rest.