This archetype is in part inspired by the Plague Doctor from Darkest Dungeon, and in part based off of the Burnt Othur Fumes poison found in the DMG.

Here it is:

At the 3rd level, you gain proficiency with the poisoner's kit, as well as the medicine skill.

Poison pods (3rd level) (here's the bread and butter)

At the 3rd level, you gain the ability to create pods of inhaled poison. During a short or long rest, you can create a number of these equal to 2 + you intelligence modifier (minimum of one). Using your action, you can throw one of these pods to a point on the ground within 20 feet of you, or 30 feet if you use a sling. On impact, any creature in a 5 foot cube originating from that point must make a DC 8 + intelligence mod + proficiency bonus constitution saving throw, or is poisoned and takes an amount of poison damage equal to your sneak attack damage (ie, 2d6 at 3rd level, 3d6 at 5th, and so on), for 1 minute. While affected by this poison, the creature repeats this saving throw at the beginning of its turn, taking additional damage determined by the "subsequent turn poison damage" table on a failed save. The effect ends early if the creature succeeds this save a total of 3 times. The poison in these pods loses their effect at the end of the rest after you made them. (this is to prevent stocking of them.)

(I realize that it is in fact sneak attack damage without having to meet the normal requirements, but Con saves are commonly very high on significantly tougher enemies, so the most damage from this would be putting it onto weaker foes at the start of a battle and dealing with the tough guys normally. On top of that it can't crit, and the lasting effect can be removed in all the normal ways. The damage might need to be reduced, but some experimentation with this will be done before saying yae or nae to that, seeing as how you give up your normal sneak attack for it, unless you pull some kind of war cleric multiclass jankiness or something. Another thing that might come up is the cost of the inspiring poison, but remember that according to the DMG, most of that price comes from taxes on poisons, and you could find your own materials to make these. Last note, poison is fairly commonly resisted.)

Restorative pods (also 3rd level)

You can forego making any number of poison pods to create that many restorative pods instead. Using one requires your action. When applied to a creature, that creature regains 1d4 hit points and all poisons are removed from it. a creature with 0 hit points doesn't regain any hit points, but is stabilized if it's dying.

(free healing items may be overpowered early on, but by third level an actual healer is restoring a lot more than a d4 using their action. The main thing here is the ever-situational remove poisons effect.)

Blinding pod (9th level)

Beginning at the 9th level, you can make one pod of blinding gas during a short or long rest. Using your action, you can throw one of these pods to a point on the ground within 20 feet of you, or 30 feet if you use a sling. On impact, each creature in a 10 foot cube originating from that point must make a dc 8 + int + prof Con save or be blinded until the end of your next turn. Like the poison pods, this pod loses its effect at the end of the next rest you take after making it.

(this one should be okay, a 1 per rest effect akin to color spray, a 1st level spell, shouldn't be overpowered by level 9.)

Poison cloud pod (13th level)

Beginning at the 13th level, you can forego making 2 poison pods to create one poison cloud pod. The cloud pod has the same effect as the normal poison pod, except it does no initial damage and fills a 10 foot cube for one round, affecting creatures on impact or when they first enter the area. You can only make one of these when you make your poison pods.

(this is limited to one per rest and is just a bit of area control, perhaps deter people from chasing you through a tunnel.)

Sickening presence (17th level)

You can use your action to release a cloud of poison that lingers around you for 1 minute. While the cloud is active, another creature that starts its turn within 5 feet of you or hits you with an attack in the same radius must make a DC 8 + int + prof Con save or be poisoned until the start of its next turn. Once you use this feature, you can't use it again until you finish a short or long rest.

(a way of shaking off aggro, not much at 17th level but i'm open to suggestions to change it.)

"subsequent turn poison damage" table
Level-------Damage
3-4 1d4
5-8 2d4
9-12 3d4
13-16 4d4
17-20 5d4

(most creative table name ever, but otherwise the idea here is to deal somewhere around 1/3 of the initial damage without having to break into some combination of d4's and d6's at every other level, to make it easier to track.)

I hope everyone hates it and can't collectively decide if it's too strong or too weak, i'll be back sometime tomorrow or the next day to check up on it. :D