Lots of games have a type of "freeze" or "ice" element effect to their weapons, like for instance cryo weapons in Borderlands, but I'm trying to work out how that might be physically plausible.
Apparently thermodynamics is extremely complicated, but there are some crude approximations with specific heat. I've tried investigating different masses and materials in simplified scenarios, different specific heats and so on and I was stumped, because realistically, the mass contained inside a bullet, or a very then film of an sword, is generally not enough to greatly cool an entire character from my preliminary research, not even if you had beyond-physically-possible conditions like below-absolute-zero temperature and 10000 specific heat outside of conditions so extreme that you'd have a difficult time explaining them.
This is generally because you need a lot of mass to cool another massive body like a character, or lot of motion like a lot of flow of a pre-chilled material to carry heat away and coming up with that energy and circumstance is also difficult to explain.
But there's one explanation I didn't explore, which is the adiabatic expansion of hyper-compressed coolant gas.
Could you pressurize enough gas with a low enough heat capacity, inside a bullet so much so that when it expanded and contacted with a character, it spread and cooled a lot of their surface in a short time to explain a cryogenic effect?