I played through the scenario with a hero. Dark magic of enslavement and berserk were crucial, and I won by using them to my advantage, taking refuge in a city and defeating demon troops with a "high" threat level. The only problem was with the mages – I had to replay the scenario about ten times because of their ability to reflect magic, as well as their defensive tactics in the city. I didn't complete any secondary quests, and I didn't fully explore the map. I defeated everyone in this way. The map is excellent, but I think it's a drawback that the Necromancer Giovanni behaves passively and doesn't attack the cities of Haven, which allows you to ignore defense and "divide and conquer." Demons are extremely passive towards dark magic castles, making them easy prey.