WishmasteR
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Due to the lack of runes, I can't learn "Fireball."
I myself played as a mage on normal difficulty and completed it without any problems, although I got stuck in some places. For example, I killed the kraken after the dwarves and the spider, and I actually felt sorry for it :)
Then I tried playing as a warrior on impossible difficulty - Darion didn't pose any particular problems, but I got stuck on the Islands of Freedom, and then "The Princess" came out... The Marshlands are really difficult, but you can leave the strongest units for later and finish them off when you come back for the indulgence. This quest is not mandatory, but it is extremely useful - with the Ruby of Angar, fairies, dryads, and demonesses become a formidable force...
And you can also engage in breeding strong units for the sake of quests - it's a very entertaining thing, if you don't overdo it ;)