Secrets of the Plague Doctors - The Armoury.

https://www.keiththompsonart.com/pages/viraemia.html

Plague Doctors! As dangerous as Skaven and Tinker Gnomes combined!

*Everything here is optional, dependent on the tech-level of the setting and on how established the Plague Doctors have become. 

D&D-adjacent/barely system agnostic.

Armoured Suit.

Equal to BECMI Scale armour (the bridge between Leather and Chain), and has the same special properties as the traditional mask-and-robe already covered in the main entry for the Plague Doctor class.

Provides a +1 to saves and -1 to damage per die to AoE attacks (as for BECMI suit armour).

A full plate version can exist (BECMI suit armour RAW - the ahistorical version).

*Can form the basis for fantasy diving- and vac-suits.

Compounds - Miasma.

Associated with the classic elements of Air and Earth, miasma is the foundation of chemical/gas as well as germ warfare in the fantasy setting.

Unprocessed miasma has all the general properties of a stinking cloud cast at lowest level,  plus exposes those in the AoE to the associated disease. 

It is most readily harvested from purulent corpses and plague pits, and most people are happy to let the Plague Doctors get on with it, rather than dig into their secrets.

Addition of phlogiston can make a miasma mixture that it lighter than air. 

*It's up to you whether this mixture is dangerously flammable or perfectly safe.

All types of miasma can be neutralised by contact with universal solvent in sufficient quantity/proportion. Also, cure disease (Plague Doctors hate this one weird trick).

Can be delivered as grenade-like missiles or by Hygienic Patented Pneumatic Applicator. You need to rinse out the Pneumatic Applicator with universal solvent between miasma loads (this does not affect reload time).

Anti-Phlogiston: Fire extinguisher (Earth smothers Fire).

Instant on normal fire; normal probability per round for phlogiston; allows a new save at advantage/bonus and -1 damage per die for dragon/magical fire - though you decide if it's actually enough to put it out.

Fire monsters suffer (radiant/cold) damage equal to being hit by Dragon's Fire (see below).

Cannot be made lighter than air, as this would require the addition of phlogiston.

"Cloak of Fear": Brand name for fear gas.

Effect last while in the AoE and for d3 rounds afterwards; all saves vs. fear, horror etc and Morale Checks are at disadvantage/penalty.

*A scarecrow-themed Plague Doctor seems a good candidate for developing a more effective fear gas.

Concentrate: Ancestor of riot foam.

Equivalent effect to the spit of the Cave Locust, Giant. 

Cannot be made lighter than air, as its effectiveness comes from its concentrated substance - treat as (AD&D) Green Slime, rather than stinking cloud.

"Fog of War": Brand name for blinding gas.

A clinging gas that cause temporary blindness to those unprotected in the AoE and for d4+1 rounds after they leave/it dissipates.

The Plague Doctors also produce eye-drops (dilute universal solution) that will clear the eyes on the round following application. 

Frenzon: Failed experimental prototype intended to remedy broken morale on the field.

Anyone unprotected in the AoE and for d3 rounds afterwards is subject to uncontrollable hideous laughter. 

A failed Morale Check during this time triggers berserker frenzy, rather than retreat.

Subjects report vivid nightmares over the following d6+1 nights.

"Plague Wind": Brand name for disease gas.

Anyone in the AoE or targeted/splashed is exposed to a disease at double normal chances of infection, with an incubation period of 1-6 turns. Check each round of unprotected exposure.

Anyone infected is a carrier, but further instances of the disease are at normal rates of infection and incubation.

Compounds - Phlogiston.

The elemental form spontaneously and instantly combusts in contact with air. It is counterintuitively unreactive to flame/heat and has a very low flash/burn temperature.

Mix it with other ingredients, however, and it can quickly get out of control.

In terms of magical/scientific understanding, phlogiston is associated with the classic elements of Air and Fire.

The Plague Doctors ruthlessly maintain their monopoly on the practical secrets of phlogiston. Their covert/plausibly deniable operations to maintain this are not so covert and deniable as to encourage persistent outside research.

The three substances below are the most common applications of this discovery. They can be delivered as grenade-like missiles or by Hygienic Patented Pneumatic Applicator.

Alchemist's Fire: Dungeoneer's Molotov; this is your basic burning oil as featured in most pseudo-medieval fantasy settings. 

Its main advantage over standard burning oil is that it is half the encumbrance.

It must be lit on fire.

Dragon's Fire: Dungeoneer's Greek Fire.

Twice as hard to extinguish (by whatever methods) and twice as fast/likely to spread as normal fire/burning oil; +1 to damage per damage die.

It must be lit on fire, but can be done so even if wet, as long as it is not completely submerged.

Hell's Fire: Dungeoneer's napalm. 

Contains components of miasma, so can be spoiled by universal solvent.

It ignites on contact with the air and will burn underwater (so ingenuity makes an aquatic flamethrower possible).

Twice as fast/likely to spread as normal fire/burning oil, and can only be extinguished with anti-phlogiston, magic or letting it burn out naturally; +1 damage per damage die.

If you are the target of or are splashed with Hell's Fire, you also suffer d3 acid damage per round until the fire is extinguished.

Devices.

Flit Gun: Weaponised clyster/ an old-fashioned bug spray from the old-fashioned cartoons.

Max. 1 charge - which comes in a handy screw on/off cannister.

Two-handed; fouls/misfires like a firearm, but you can just replace the cannister as a normal reload to correct this.

Spray or cloud, but it's only 5' range/AoE - you will be caught in the splash, so wear your beaky mask and hazmat suit.

Hygienic Patented Pneumatic Applicator: Medical grade flamethrower.

Max. 6 charges, but randomise in secret as the mixture and the process are inconsistent: d6 for a single or untrained operator; d3+3 for a team of 2 Plague Doctors.

It is bulky, heavy, two-handed and misfires/fouls like a firearm. Potential to explode (AoE and damage depends on how many charges left).

It is slow to reload, even with a crew of 2; otherwise, it takes twice as long.

One charge can produce a 20' line/cloud (depends on substance), but d3 charges must be expended to produce a 20' cone.

A line target is the centre of a splash effect; everyone in a cone is a target, no splash.

Basic damage for the flamethrower is 2-12 (or as appropriate for burning oil in the setting/system), adjusted for whether it's Alchemist, Dragon or Hell's Fire. 

Dragon's Fire needs to be rinsed out with universal solvent for each reload, or the chances of misfire/fouling are doubled (this does not affect the reload time).

Because of its pre-burn consistency, Hell's Fire doubles the chance of misfire/fouling, but does not need to be rinsed out between uses.

Plague Censer: Pole-and-chain-mounted thurible used to burn and distribute miasma-based compounds.

Once lit, compounds burn for d6 exploration turns unless extinguished and produce a 20' cloud in one round. 

Effects are as for exposure to the relevant miasma. If you make your first save, you make others thereafter at advantage/bonus; three successes in a row, and you don't have to make any more vs. this batch.

As well as being less effective than other methods, Plague Censers are considered old-fashioned and/or unscientific, having their origin in the bale- and need-fire traditions of the past. 

Reinforced Bellows: Weaponised clyster.

Max. 2 charges.

Two-handed; fouls/misfires like a firearm; slow to reload. Line or cloud, depends on substance used.

If using Alchemist's or Dragon's Fire, you lose Initiative if you do not have an assistant to apply a lit match as you squeeze the bellows.

Half the range/AoE of the Hygienic Patented Pneumatic Applicator. You are at risk of being caught in the splash/cloud zone.

Does not need to be rinsed with universal solvent after using Dragon's Fire, as long as you're just reloading it with more Dragon's Fire.

Being a much simpler device than the flamethrower, the risk of fouling/misfire with Hell's Fire is not doubled.

Goggles/Lenses.

*Enlarging and focusing lenses are no better than 50% the strength of eyes of minute seeing or eyes of the eagle, but I've not done research on ancient to early modern period lens quality.

Blackened: You cannot see through them except when they give you auto-save vs. light-based and gaze attacks.

Stage -6 Nocturnal/Heliophobic Plague Doctors can see through these lenses as well as being protected from the light.

Frosted: Reduces everything to shapes of light and dark.

Protection vs. gaze attacks; hindered 50% as much as if you were averting your gaze.

Mirrored: As Frosted, but with a 10% chance of reflecting gaze attacks.

Must save vs. fire each time they are exposed or lose their mirrored property.

Smoked: Sunglasses; advantage/bonus vs. dazzle and snow-blindness.

Stage -1 Nocturnal/Heliophobic Plague Doctors can offset their penalty while wearing smoked lenses.

Stage -3 reduce their penalty to -1 and make saves vs. light-based attacks normally.

Grenade-like missiles (Vial Bombs). 

Basic rules as for the setting/system. Splash/cloud radius is normally/nominally 5'.

Delivers a dose of phlogiston or miasma with the relevant effects, though grenade-delivered miasmas will dissipate in normal conditions within 3 rounds (2 if it's raining, 1 if it's windy). This is a function of volume, so dumping a load of grenades at once or in quick succession could get a proper stinking cloud going.

You can also fill them with acid, holy/unholy water, and universal solvent.

Not forgetting the example of Darkest Dungeon:

Disorienting blast causes 2d6 non-lethal damage and save vs. temp. deafness in splash radius. All in 10' (30' in darkness) must save or be dazzled d3 rounds (no save if surprised; low intelligence light-hating monsters will probably retreat).

Noxious blast causes d8 non-lethal damage to the target and d4 splash; save or nauseated as for a lowest-level stinking cloud (advantage/bonus if only splashed).

Plague grenade is the same as the noxious blast, but everyone hit is exposed to a disease at disadvantage/penalty. They are a somewhat old-fashioned weapon, dating back to before miasma could be refined and the disease component separated off.

Substance - Universal Solvent.

Carbolic steam spray - antiseptic and caustic.

Universal solvent can be put through the Hygienic Patented Pneumatic Applicator, and can be used as a line or a cone. Addition of phlogiston allows deployment as a cloud.

As well as neutralising miasma (target, splash and AoE), it will kill all small animals of 2 hp or less (save allowed if appropriate). 

Larger animals (including humanoids) are affected as the rash component of an irritation spell and must save vs. temp. blindness (advantage/bonus if only splashed). If it's a line or a cone, they suffer d3 damage on the first round, 1 hp on the second (unless immediately doused in water); if it's a cloud, they suffer 2 hp on the first round, 1 on the second, and make their save vs. blindness at disadvantage/penalty.

As well as a pesticide, it is also an effective weedkiller - plant monsters suffer (necrotic/acid) damage acid equal to being hit by Dragon's Fire, and this can only be healed with Druidic magic.

Disease/parasite monsters suffer similarly, but can heal from this damage at half-rate.

Syringes.

The main effect will be from whatever you've loaded them with. 

If you're using onset times, then a syringe is at least 50% to 100% faster than ingestion.

Fine (Glass) Syringe: Recognisable as vintage drug paraphernalia. Needs a padded case, but barely encumbering.

0 damage  + special vs. S and M targets; no effect vs. L. 

Breaks on a successful hit, or an odd-numbered miss.

Crude (Metal) Syringe: The old-fashioned type; crude in comparison. Needs a cork on the end to carry safely; about as encumbering as a dagger/iron spike.

1 lethal damage + special vs. S and M targets; crit only vs. L.

Breaks on an odd-numbered miss.

Two-handed Syringe: Modified clyster. Reservoir for max. 3 doses. Too awkward to conceal; about as encumbering as a hand axe/mace.

As dagger + special vs. S, M and L targets.

Fouls on an odd-numbered miss; d3 rounds to resolve.

Syringe Thrower (Tranquiliser Gun): Two-handed projectile device; short range only; ammunition cannot be reused, hit or miss.

As Light Crossbow for Fine (Glass) Syringes: 1 hp + special.

As Heavy Crossbow for Crude (Metal) Syringes: d3 hp + special.

Commentary.

Are there any medical dictatorship settings?

How about an alternative Krynn, with the Plague Doctors emerging post-Cataclysm? 

You bet the Plague Doctors would be up to their neck's in it in undead-apocalypse settings, for better or worse.

Bearing in mind the necromantic inclinations of the Plague Doctors and the different relative standards of magical integration across settings, they could also add necro-tech to their arsenal.