Quests and puzzles!

Unfortunately, I was working all day, and yesterday I also didn't have much time to think before going to bed. But today, while at work, I started to consider 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 afternoon. So, the first: 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 isn't very much (according to FizMIG, the maximum damage from Titan's Thunder is 1764 HP), but:
a) mana is not needed at all!
b) magical power, the presence, and the level of development of the Air Magic skill also don't matter!
c) it also doesn't matter what the hero's Knowledge skill is!
The rest is clear: attack the dragons with Titan's Thunder until they are completely destroyed!
The second possibility: as heroes13 already said, blind the dragons, summon elementals (preferably earth elementals, of course), strengthen them, weaken the dragons, and cast a fire shield on the elementals. You can also "reduce" the dragons' defense to 0 with a destructive beam.
But here, the main thing is to try to calculate or experiment (if someone has enough time), because I strongly suspect that the hero may not have enough mana for 9999 Crystal Dragons. In addition, elementals cannot be summoned in any quantity:

When the object counter reaches its maximum (which is 20 objects for each side), no other object can appear on the battlefield - you cannot raise Demons, summon Elementals, or create a Clone.

(again, FizMIG)