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I'm replaying the original game's campaigns on version 3.1 with NCF. The difficulty level (default) is Hero. I encountered problems in some missions, such as the beginning of the third mission for Rai'lag, the "Emerald" missions for Faidaen, and a few others, only because I chose the wrong tactics. If you think through where and what to do, they can be completed quickly.
P.S.
And the campaign for the mage was enjoyable: in missions 1, 2, and 4, I fought with undead troops ;). The converter rules the world!