"The Will of Ashan" - "Heart of Darkness" [2nd campaign, 5th mission]

I'm playing on "Heroes 3.1". The final battle is a pain. I went through the entire map without entering a castle even once. And now I have to skip turns – accumulate money, then move my army to the Necropolis, then bring the army to Arantir... Ugh... And I'm stuck, I can't defeat him with my modest demon army because he has a cheating ability – I cast it on his troops, + artifacts -8 morale, his troops get -5 morale, and it doesn't work. Negative morale never triggers, it's a normal week, I checked. And the initiative of his troops is a hundred times better than mine; in two rounds, they kill an army of 200 princes and others. I'll have to save up gold for 2 weeks and storm it. Damn, that's sad... But wait, the path through the liberated portals to the undead castle is only 2 days. I'll just buy angels and griffins and try a combination of dragons + vampires.