Terraniux
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Unfortunately, I worked all day, and yesterday I didn't have much time to think before going to bed. But today, during the day at work, I started to realize what else is needed to solve this problem.
In addition to what I said earlier, there are two possibilities. The first one is definitely sufficient without calculations; I'm not sure about the second one. We can calculate it tomorrow during the day.
So, the first one: everything is the same as I suggested before, but our hero must have Titan's Thunder. The base damage from Titan's Thunder is 600 HP, which is not very much, but:
a) no mana is needed at all!
b) the magical power, the presence, and the level of development of the air magic skill are also not important!
c) it also doesn't matter what the hero's Knowledge skill is!
The rest is clear: hit the dragons with Titan's Thunder until they are completely destroyed!
In fact, I think we can congratulate comrade Marmot on his victory!!
He voiced the main idea, although there are still several significant nuances, but I am sure that he will figure them out and name them!