Poisonmonger

In the black markets of Faerûn, there are many unsavory folks. Some that sell illegal weaponry, imported drugs, or even people, in the worst of cases. But the true kingpin of the underworld traders is the poisonmonger. Appearing to be a simple poisons peddler, a poisonmonger is never seen as the bigger threat by those who are coming into the criminal underworld for the first time, but when you need a man in power dead, they should be the first person you go to. Never underestimate what can happen when a nobleman ingests even a single drop of this criminal's specialty product.

First, the vision blurs, and the feeling of pins pricking your skin begins to spread all over your body. Then, you feel as though your throat is seizing up, spasming open and closed rapidly. Then, you drop to your knees, as you spit blood all across the floor. Boiling blood. And the last thing you can see, as you fall limp into a pool of your own crimson fluids, will be the man in the back of the crowd, quietly nodding to himself as he walks away. A job well done.

Toxicologist

When you choose this archetype at 3rd level, you gain proficiency with the poisoner's kit. Additionally, whenever you make an Intelligence (Arcana) or Intelligence (Investigation) check to discern whether or not something is a poison and/or the type of poison, you gain advantage on that ability check.

Lethal Injection

Also at 3rd level, you gain the ability to use your poisons in combat, granting you the following benefits:

• You can use the bonus action granted by your Cunning Action to apply a special poison to either a weapon, or a single piece of ammunition. If applied to a weapon, the weapon must deal piercing or slashing damage, and must have the light, thrown, or finesse property. If applied to a single piece of ammunition, the ammunition must be for a ranged weapon that deals piercing or slashing damage. This special poison causes the next attack made with the applied weapon/ammunition to deal an additional 1d6 poison damage. If the attack made was a sneak attack, it instead deals an additional 1d10 poison damage. A weapon/ammunition can only be coated with 1 layer of this special poison at a time.
• You can use the bonus action granted by your Cunning Action to apply any injury-based poison you have to your weapon.

Potent Toxins

At 9th level, your specialty poison grows in power as you learn to craft more potent side-effects. Whenever you deal damage with a weapon coated in your special poison, the creature must make a Constitution saving throw (the DC of which being equal to 8 + your proficiency bonus + your Intelligence modifier), or else become afflicted with the poisoned condition.

Whenever you afflict another creature with the poisoned condition, they take 1d4 poison damage at the end of each of their turns, until they become no longer poisoned.

Shady Business

At 13th level, your empire of poisons grows ever-larger, and your ability to create and sell these poisons grows with it. Whenever you make a Charisma (Persuasion) check, you can choose to use your Intelligence modifier instead. Additionally, whenever you use your poisoner's kit to create poisons, the gold you must spend to create the poison is halved.

Impeccable Poisons

Starting at 17th level, your genius ability to use poisons becomes the best in the business, allowing you to kill what should be the unkillable. You can use the bonus action granted by your Cunning Action to apply ingestion and contact-based poisons you have to your weapons/ammunition. These poisons are treated as injury-based poisons when applied to your weapons/ammunition in this way. Additionally, your special poison gains the following benefits:

• When a sneak attack is made against a creature with a weapon/ammunition coated in your special poison, it deals an additional 2d10 poison damage instead of 1d10.
• When a creature fails the saving throw from taking damage from a weapon/ammunition coated in your special poison, their poison resistance and immunity is suppressed, and their immunity to the poisoned condition is suppressed. This lasts until the poisoned condition applied by this special poison is removed from the creature.
• When a creature takes the 1d4 poison damage at the end of their turns from being poisoned by a weapon/ammunition coated in your special poison, their hit point maximum is reduced by an amount equal to the damage taken. This lasts until the poisoned condition applied by this special poison is removed from the creature.