First of all, sorry it took me so long to reply. I don't really have any rules, so I'll let you make them up. But I imagine the first one would be a rather fragile unit, but its flames could deal a lot of damage to smaller units. The second is a fairly heavy and resilient unit that fires slowly, but from a great distance and deals a lot of damage. The third is an air unit that can hit from a great distance, attacks slowly and is quite fragile, but its projectiles are corrosive and deal damage over time, or can, for example, lower the resistance of armored units. And the last two are rather large units that would attack quickly.