ZveroBoy
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You forgot that with the Beastmaster, you can revive a hero by pressing the spacebar. And on this map, you can manage without it. Attack with a hero near the city gates, gain mana, and let him die. Revive the hero, and so on. In my playthrough, I got 100 mana.
Added 5 minutes later
I don't quite understand you. If, after building the Vampires, you then go to the Fortress for Vampiric Strike, you can forget about getting into the boat on days 6-7. Is that right?
You'll have to get into the boat without the Vampires and capture the Nature Fortress
without the Vampiric Strike, but once you capture the second Fortress,
you can buy a third hero there, and Sandro should die.
Then they should escape from some battlefield with Sandro's corpse,
it will revive in its Fortress, learn Vampiric Strike there, and then go back to the Nature Fortress. That's what I meant.
Iron.
Spike Iron is right; you just need to attack
Leprechauns with one Imp and two Skeletons so that the Leprechauns split into four groups, and then make sure the Imp efficiently drains mana from them, and do this 27 times (27*12=324).
I thought you had already stopped playing my tournament. :)