Poisoner

A few drops slick the blade of a training sword, a hand quickly passes over a jeweled goblet, a merchant blows perfume into the face of a passing noble.  Moments later, a knight falls out of the saddle writhing in pain, a king's face hits the banquet table, and a noble is slain by his own frenzied escorts. 

Poisoners are as deadly as they are untraceable, dispatching their enemies both brutally and discreetly.

Trained in Toxins

When you choose this archetype at 3rd level, you gain proficiency with the poisoner's kit.

Whenever you finish a short or long rest while you have your poisoner's kit on your person, you can create a Vile Toxin in an empty flask you touch.  Using your Cunning Action, you can apply the toxin to one slashing or piercing weapon or one piece of ammunition.  When you hit a creature with the affected weapon or ammunition, the weapon or ammunition loses its potency and the creature must make a Constitution saving throw (DC equal to 8 + your Intelligence modifier + your proficiency bonus).  The target takes poison damage equal to your Sneak Attack damage on a failed save, or half as much on a successful one. 

Vile Toxins lose their potency when you begin a rest.  Only you understand how to properly store and apply your Vile Toxins, and they lose their potency immediately if used by a creature other than yourself.

When you reach certain levels in this class, you can make more Vile Toxins at the end of a rest: two at 9th level, three at 13th level, and four at 17th level.

Venomous Versatility

Starting at 9th level, you have experimented with new ways to apply your Vile Toxins to unsuspecting victims.  When you create a Vile Toxin, you decide whether to make it applied via injury, inhalation, or ingestion.

Injury.  Injury Vile Toxins can be applied to piercing or slashing weapons or pieces of ammunition.  A creature that takes piercing or slashing damage from an object coated with the Vile Toxin is exposed to its effects.

Inhaled. Inhaled Vile Toxins are colorless, odorless powders or gases that take effect when inhaled. Blowing the powder or releasing the gas subjects creatures in a 5-foot cube to its effect. The resulting cloud dissipates immediately afterward. Holding one's breath is ineffective against inhaled Vile Toxins, as they affect nasal membranes, tear ducts, and other parts of the body.

Ingested. Ingested Vile Toxins are colorless and flavorless liquids.  A creature must swallow the entire dose to suffer its effects.  Once a creature suffers the effects of an ingested Vile Toxin, it is immune to its effects for 24 hours.

Also at 9th level, you can create a second Vile Toxin when you finish a short or long rest.

Infectious Ingredients

By 13th level, you have studied hundreds of poisonous herbs and minerals, adding the most interesting options to your poisoner's kit.  When you create a Vile Toxin, you can add one of the following effects:

Blood Rot.  The target takes necrotic damage instead of poison damage.

Vile Delirium.  On a failed saving throw, the target takes no damage from the Vile Toxin, but behaves randomly as if subjected to the confusion spell for one minute.  At the end of its turns, it can repeat the saving throw, ending the effect on a success.

Deadly Neurotoxin.  The target makes an Intelligence saving throw instead of a Constitution saving throw.

Assassin's Blood.  On a failed saving throw, the target is also poisoned for one minute.  At the end of its turns, it can repeat the saving throw, ending the effect on a success.

Lingering Malady.  The Vile Toxin retains potency for one additional attack after hitting a creature.  The target of the second attack takes half as much damage on a failed saving throw, or no damage on a successful one, then the Vile Toxin loses its potency completely.

Midnight Tears.  The target suffers no effect immediately, but takes twice as much damage at the stroke of midnight.

Also at 13th level, you can create a third Vile Toxin when you finish a short or long rest.

Vile Virtuoso

Starting at 17th level, mixing the right reagents into your Vile Toxins is second nature to you, to the point that you can do it in the middle of combat or in a crowded chamber.  When you create your Vile Toxins at the end of a long or short rest, you no longer select options from your Venomous Versatility and Infectious Ingredients features.  Instead, you choose which options to apply to your Vile Toxins when you use them.

Also at 17th level, you can create a fourth Vile Toxin when you finish a short or long rest.

Perfection in Poison

Also by 17th level, your knowledge of poisoncraft is unparalleled, and you can guarantee success.  When a creature you can see succeeds on a saving throw against your Vile Toxin, you can use your reaction to make it fail instead.  Once you use this feature, you can't use it again until you finish a long rest.