The opening sentence sounds like what’s happening in Ukraine. xD
Catastrophic real-world events aside…
This involves MAJOR spoilers for Kandosii Beroya’se, one of my games, so for my players, you’ve been warned—stay away.
Night Breath was developed by Lok Durd as a biological extermination agent, designed to annihilate clone troopers AND Jedi (with civilians being an un/fortunate side effect, depending on your perspective).
Expanding on his previous projects as a base, Lok Durd tapped into some ancient knowledge from Sith Alchemy (relayed to him via a dark Jedi and his Sith holocron) to increase the potency of his weapon. Released as a gas, the black cloud billows out rapidly, killing everything living that it touches almost immediately. How? By targeting midichlorians. It binds with them and kills them, subsequently destroying the host.
Plants, people, kyber crystals—all dead. More Force-attuned (read: higher midichlorian count) beings show significantly more external damage. Once the weapon has run its course and the cloud decays, it leaves behind a thick layer of black dust which is relatively non-toxic. Exposure gives no harmful effects beyond what could be expected from breathing in large quantities of ANY dust.
Oh, one more thing: The compound actually works like putting food dye in water. When released to the atmosphere, the atmosphere itself serves to propagate the weapon, out to the maximum range of the quantity brought. In the case of the game, several canisters were used to kill the crew of a Venator as an experiment.
This project was subsequently shut down (for multiple reasons), and Lok Durd eventually went rogue. He paid to have Nuvo Vindi broken out of jail, and they continued to perfect the weapon, as well as various other projects.
Lok Durd created an unnamed “damotite bioweapon” on Lanteeb.
Nuvo Vindi manufactured the Blue Shadow Virus
The Separatists experimented with Trihexolophine1138, which was accidentally released on Honoghr
The Separatists used “Swamp Gas” on Ohma D’un, killing the Gungan inhabitants.
These were just the ones I could think of off the top of my head, and was personally aware of. If you want more examples, I’d suggest looking through this Wookieepedia category and its sub-categories: Category:Biological weaponry | Wookieepedia | Fandom