Blightdrinker

Almost all rogues will have at least a passing familiarity with poisons, but very few have as intimate a relationship with them as blightdrinkers. Through constant study and application, blightdrinkers have not just inured themselves to poisons and other ill-meaning solutions, having turned their bodies into crucibles from which toxic stews are cultivated. From even the most deadly of afflictions, the blightdrinker derives perverse advantage, altering body and mind.

Poisoner's Gift

Starting at 3rd level, you can use the bonus action granted by your Cunning Action to apply poisons to weapons, items, your body, for the purpose of unarmed strikes, or drink. If a poison that was applied to your body would cause an effect on you, such as contact poisons, you would suffer the effects of it as normal but you don't use up the poison and can still be used during an attack. You gain proficiency with the poisoner's kit.

You can also spend 1 minute using your poisoner's kit to concoct an antidote. When a creature drinks the antidote, it removes one disease or the poisoned condition if it is afflicted by it. Once you use this ability, you can't use it again until you finish a long rest.

Corroded Heart

 When you choose this archetype at 3rd level, you gain resistance to acid and poison damage.

In addition, when you take poison damage, you gain temporary hit points equal to your Intelligence modifier after taking the damage.

Spoonfuls of Death

Starting at 9th level, you regain health when you drink poisons. Poisons that you ingest that would normally deal poison damage doesn't damage you. When you drink ingested type poisons, you instead regain 4d4 hit points. If you drink other types of poison, you regain 2d4 hit points instead. At 17th level, the regained hit points become 8d4 and 4d4, respectively.

In addition, when you're poisoned, instead of disadvantage on attack rolls and ability checks, you gain advantage.

Venomous Dirge

By 13th level, your very existence is so polluted, that it is nigh indistinguishable from the chemicals inside. You can use the reaction granted by your Uncanny Dodge to instead take the full damage of the attack, and expel noxious gas from your wounds in a 15-foot cone. Each creature in the cone must make a Dexterity saving throw, taking 2d8 acid and 2d8 poison damage on a failed save, or half as much damage on a successful one. The DC is equal to 8 + your proficiency bonus + your Constitution modifier. Any creature that fails this also gains the poisoned condition.

In addition, your near preternatural attunement to poisons and diseases allows you to detect their presence, location, and types. You can cast detect poison and disease and regain ability to cast the spell again after doing a short rest.

Plaguebearer

When you reach 17th level, you can become plague-ridden at the cost of your health. You become drenched in the corrosion and poisons that has been brewing inside you.

As a bonus action, you take damage equal to half your current hit points and you gain the following benefits for 1 minute:

• You have advantage on all saving throws against conditions.
• All of your attacks deal acid or poison damage instead of weapon damage for the duration.
• Your movement speed increases by 10 feet and your Armor Class increases by 2.
• When you hit with a melee attack, you deal extra damage equal to your Constitution modifier.

This ability ends early if you are knocked unconscious or regain hit points from any source except poisons. You can also end it using a bonus action. Once you use this ability, you can't do so again until you finish a long rest.