Cryogenic weapons

This is impractical instead of unrealistic because we can make weapons/tools that lower temperature of things even at a distance, however, the required energy, resources and time to do so make it extremely inefficient compared to other methods of killing people. The most feasible way of achieving a cryogenic weapon would be to just hose the targets with liquid nitrogen or similar, but even that is extremely impractical. So in short, we can make them, it's just not worth the effort.

NOTE: This does not include weapons that shoot shards of ice unless the said shards additionally freeze the things they hit.

See also: freezing, cryokinesis
Contrast: thermal weapons