Almost all rogues know something about poison, but as the name suggests, for Poisoners, it is their primary area of expertise. The stereotype paints these experts in toxins as pitiless killers and for some, this is chillingly accurate. However, for others, the allure of poisons is that they can debilitate without killing. A little belladonna here, a little curare there and a clean getaway is facilitated and nobody has to die.
Beginning at 3rd level when you take this archetype, you become proficient with the tools of the poisoner’s art. You gain an expertise die to checks made with the poisoner’s kit, and if you fail a check to harvest poisons, you do not risk poisoning yourself. When you successfully use your poisoner’s kit to harvest poisons, you harvest additional doses equal to half your proficiency bonus.
You also are especially adept at slipping substances onto innocuous items and into food and drink. You make all Stealth, Deception, and Sleight of Hand checks to conceal poison, drugs, potions, or similar substances in food, drink, or on unattended inanimate objects with advantage.
Also at 3rd level, you learn to use toxic substances to maximum effect in combat. You gain proficiency with the Viper’s Fangs combat tradition and learn a first-level Viper’s Fangs maneuver which does not count against your number of maneuvers known.
You also gain proficiency with blowguns.
Beginning at level 9, your continued exposure to toxins and chemicals alters your physiology. You are resistant to poison damage and your blood becomes toxic to other creatures. Whenever another creature hits you with a bite attack, it takes 2d6 poison damage.
You can also use your own blood as a means to fuel your abilities. If you would use basic poison, you may spend your reaction to deal 1d6 points of necrotic damage to yourself, allowing you to use your own blood as a single dose of basic poison.
Beginning at 9th level, you learn the Virulent Stance maneuver and you are always under its effects. It does not count as an active stance for you, does not cost exertion, and affects any poison you use, not just named ones. If you already had the Virulent Stance maneuver, you may select another Viper’s Fangs maneuver in its place. If you would deal poison damage, you can choose to do acid or necrotic damage instead.
At 17th level, you learn a truly insidious trick: the ability to turn your enemies into a walking trap. When you hit a creature with an attack and do not have disadvantage, you can spend 1 dose of advanced poison to mark that creature with a poisonous sigil.
Alternatively, you can spend 1 minute to imbue an item of food or drink with a minor magical effect which marks the next creature to consume it. The next time a marked creature is within 10 feet of another creature friendly to it (which can either be a specific creature you specify or any of its allies, at your option), the sigil detonates, filling the area within 20 feet of the creature with poisonous gas. A creature that enters the gas or begins its turn in the gas must make a Constitution saving throw, taking poison damage equal to the bonus damage from your Sneak Attack feature on a failed save and becoming poisoned for one minute. A creature that succeeds on its saving throw takes half damage and is not poisoned.
Once you have used this ability a number of times equal to your Intelligence modifier (minimum once) you cannot do so again until you finish a long rest. The mark persists for a number of hours equal to your Intelligence modifier (minimum 1) and then dissipates on its own. It may also be dispelled as if it were an 8th-level spell.
In addition, you are immune to poison damage and the poisoned condition.