I was thinking about creating an ice dragon for my world, but I didn't want the dragon to be magical or technological but biologically correct, so I went looking for cryogenic substances and found some very interesting ones, they are liquid hydrogen, liquid nitrogen and liquid oxygen.
Hydrogen struck me as a good candidate, -253º C temperature, it's not toxic... But it's flammable, the dragon will be used as a war beast by a rider, so if an ally is too close to fire and that dragon attacks an enemy equally close, the ally may be injured or die as the fire will expand.
Liquid nitrogen also seems like a good candidate, it's not flammable, it's not toxic, it has a temperature of -196º C, it has an abundance in the atmosphere...
I also thought about liquid oxygen, it's also not toxic, it's also not flammable, it's also abundant in the atmosphere, it has a temperature of -183º C... However, despite not being flammable, it encourages burning.
So I chose liquid nitrogen. The dragon will have a cryogenics system. The stages of this system are: third nostril, with it the dragon can take part of the air to start the nitrogen production process; liquefaction chamber, this is where the process of liquefying nitrogen will begin, I still don't know how this will be done, I need to research more about how it's done to try to find a more biological alternative; collecting water, the dragon can open a second "throat" (I don't know what the correct term would be) which it will use to drink water and store it; release, the dragon has two tubes in its mouth, one on each side, one releases liquid nitrogen and the other releases water, this will freeze the water that can be used for attack and defense, the dragon can choose which of the two substances to release and also the amount, for example releasing much more water than nitrogen. I also don't have a way to make the dragon not freeze with something at -196°C inside it.
Well, having said that I would like to ask: what do I need to change in my dragon for this to be plausible? There is no need to use hypotheses involving theory of evolution, that would limit the creature's plausibility too much(more than it already limits). If you want, you can use hypotheses involving the theory of creation or genetic mutations alà InGen. What's important is that the dragon's cryonics system doesn't rely on magic or technology.