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Regarding the battles: I'll briefly describe them; they aren't that difficult. And after saving at point 2, you need to immediately load save 2.2; save 2.1 isn't the right one for this. Against the zombies: 1st turn: archers fire half their arrows at the regular zombies, spearmen and skeletons attack the strongest zombies. 2nd and 3rd turns: archers fire all their arrows at the regular zombies. On the 3rd turn, pause and have the skeletons attack the regular zombies, and finish them off with the spearmen (it depends on the damage of the skeletons and the zombies' counterattacks, but it might even be possible to do it without any losses, although usually you'll lose one). Then, once, have the archers take out the upgraded zombies, and the spearmen and skeletons retreat in a circle. On the 5th, 6th, and 7th rounds, run away from the zombies until you have enough movement points left, fire once, then run again, and keep doing that until the arrows run out. You'll be left with approximately 4 upgraded zombies – take them out with the spearmen while paused; the zombies won't even be able to kill one of your units in response. At the beginning of the turn, finish off the remaining zombies with the spearmen. It requires a little patience; it won't all work out on the first try, but the terrain is good for the battle, and there are no problems with retreating.
The bird battle is a little more complicated, but it will be faster. You'll need to replay it 3-4 times, depending on how their morale drops and whether they start attacking the demons on the 3rd turn. The idea is: the main group of spearmen should be protected. In the 1st round, protect with the demons. After the birds' turn (they deal single-target damage), attack a stack of 6 birds with a single unit. Then, use the plasma mage, along with the demons and spearmen, to destroy the entire stack. At the end, the main group of spearmen should be protected; then the birds will attack the remaining single unit. On the last turn, you can immediately attack the stack of 5 birds with the plasma mage; their counterattack won't be enough to even damage one elemental.
The most difficult battle is against the champions; if anyone wants, I can describe it tomorrow.
Sir mrshch, don't despair! After playing a dozen tournaments and regularly watching replays of the winners, you'll be able to win these battles easily in just a few minutes. Good luck!