HIVE

but I didn't really understand, is that a player controlled unit or a boss? If so, what forces are under player's command?

First you encounter it as a boss, then you get to control one on a mission or two, at least that's whats planned at this point

but how you encounter it, with your own air fleet or they bomb your base?

with your own air fleet, your goal is to prevent it from getting to your base because once it does the base may not last a minute

but how do other airships look like?

originally it was planned to be these: https://www.hiveworkshop.com/threads/dwarven-multi-purpose-airship.100099/#resource-25893 and https://www.hiveworkshop.com/threads/arcanegunship.270286/#resource-37282 , but I'm not sure yet. The idea is that the player gets to control 3 types of units: fighters (only target air), mixed unit (targets both air and ground but is weak hp and attack wise), and bombers (heavier armed units which can only target ground units, but are very effective against buildings)

if the whole project isn't centered around airship idea, then I suggest to cut some airship type, namely that mixed unit and maybe giving fighters a weak ground attack. But what is that ammunition of these airships, do the fire cannoballs, arrows, magic bolts or boulders?

ammunition would be some sort of magic missiles, maybe arrow, primitive bombs, nothing too mechanically advanced, not too sure at this point since its basically undergoing revision

the aerial units you use in this mission would not be available in other missions in the campaign, also we had this idea of using a phoenix instead of a heavy bomber, we basically modified the burning oil ability and made it so that the pheonix's attack burns the ground along with everything on it, pretty awesome but really op at the same time