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Fellow heroes! I want to warn you about a mistake I made. Don't take the Railaga magic skill for summoning! He doesn't need it at all; Chaos is more than enough. I didn't use summoning even once during the entire campaign.
Ideal build: Defense (it's actually useful; the troops need to hold out while the hero takes care of everyone), Logistics (it's worth leveling up for all heroes), Chaos, Sorcery, Education (you'll have a lot of mana, and the stats will be much higher).