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I played through it for the first time as a Knight. I decided to replay it as a Hero, aiming for a flawless victory (no losses at all). It took me about 18 months. The most difficult battle was breaking through the swarm of jumping demons on the road to the Elven city – they kept trying to jump towards the archers, and there was nothing to revive them with at that moment, and retreating was not an option – gold resources were depleted. After that, it became easier. Attached is the final battle with the demon lord and the army at the end of the game. The hero's skills are: Morale (Empathy), Darkness, Light (Storm Wind), Sorcery (Wisdom, Fluctuating Mana), Logistics (Keen Mind).
P.S. IMHO, the alchemy bonuses need to be toned down somehow – perhaps by introducing a usage limit. Otherwise, a hyper-super-puper lord of the underworld becomes no more frightening than a milk pig under such circumstances – not to mention ordinary neutral creatures.