I’ll preface this with the fact that I’m not too sure if the chemistry for this can be easily achieved by living creatures, but giant, flying, weaponized breath lizard, so it might be within reason.
Ernaline’s Quick and Dirty Guide to Monster Hunting.
Genus: Draco lacrimam
Known for it’s toxic breath, the choking dragon or “choker” is one of the harder monsters to fight.
The choker lives primarily in swamps, bogs, and other forms of wetlands. When not found in these places the choker tends to be found near large sources of stagnant water, this makes it a danger to farmers of rice patties.
The primary weapon of the choker is its poisonous breath which is comprised of chloropicrin. The signs of choker poisoning are: pain in eyes and lungs, shortness of breath, extreme tearing, coughing, choking, vomiting, diarrhea,headache, dizziness, fatigue, and pulmonary edema (possibility resulting in death not from chomping).
The poisonous gas will gather at the ground allowing the choker to fly safely over sprayed areas.
Attempts at creating protective devices that work on choker poison have thus far proven unreliable at best. Most masks do not provide resistance to the gas and the more effective masks are only partly effective. As an added bonus the chokers gas makes creatures vomit which leads to the removal of the mask or to drowning in vomit. Rapid dispatching of the choker is the advised route if you have access to an advanced mask.
The choker stores its poison in a bladder running down its throat to its pelvis. This poison bladder contains the liquid chloropicrin. The choker constricts this poison bladder while rapidly exhaling to produce its gas breath. Examination of choker carcasses has reviled a second set of eyelids, these eyelids are transparent and are credited with why the choker does not seem to have its vision affected by its own gas. A consensus on why the choker does not seem to be affected by breathing the gas has yet to be reached. The leading theory is the choker merely holds its breath while using its poison.
The choker is believed to have developed its breath weapon due to its habitation in swamps. The chloropinrin that has been harvested from slain chokers has been proven to be a broad spectrum antimicrobial, fungicide, herbicide, insecticide, and nematicide. The choker will breath its poison on itself at least once a day to kill off any parasites that try to take root in its hide.
Chokers can be harvested for its poison by siphoning out the liquid from its poison bladder. Caution must be used while hunting to claim more than a few drops of chloropicrin from the carcass since attacks to the front of the choker can pierce its poison bladder. Harvested poison must not be boiled unless an explosion is the desired result. The poison is highly corrosive to many plastics and rubbers as well as steel and iron which makes handling and processing of it difficult, copper brass and bronze have proven resistant to corrosion though.