Cryogunner Legionnaires are Fatui Skirmishers that attack by spraying frost from their cannon while slowly walking towards their target. They can also perform a leaping attack much like large Slimes, which inflicts area of effect damage when they land. They will also perform a belly flop charge attack if the player strays too near.
A Cryogunner can generate Cryo elemental armor to grant themselves a massive damage reduction and immunity to the Frozen reaction when inflicted with Hydro. They also gain the ability to spray their targets in an arc while walking slowly, dealing continuous Cryo damage unless one manages to circle around them to avoid this; however, the armor can be effectively stripped away with Pyro elemental damage; doing so will leave the gunner stunned and vulnerable to attacks, which you should take advantage of, usually through Elemental Reactions.