Hydrogunner Legionnaires are Fatui Skirmishers that attack by launching blasts of water from a distance. Due to their slow speed and low attack frequency, Hydrogunners are not a major threat on their own. However, in many encounters, they're accompanied by other Fatui skirmishers, and because they can heal their comrades, Hydrogunners should be targeted first. Similarly to their Cryo counterparts, they will also perform a belly flop charge attack if the player strays far away from them.
A Hydrogunner can generate Hydro elemental armor to grant themselves a massive damage reduction and their healing effect on their allies is also capable of applying health regeneration to them. While the shield can be frozen with a Cryo Element to interrupt them, the best way to strip their armor is by attacking them with Electro attacks.