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No one wants to describe how to play the "Days of Flame" scenario on the HERO difficulty level. So, I'll tell you.
1. Restart until you get the artifact, a sword with +2 attack, as a bonus, and immediately rush to the Fortress of the Wood Elves, only recruiting sprites along the way; don't pick up resources yet, and capture the fortress. Then, gather all the resources and artifacts around the fortress, and capture the mines.
2. Under no circumstances should you capture the second Wood Elf fortress; you won't be able to hold it (on the Hero difficulty level).
3. Try to start building with money-generating buildings. When you build dragons, the Blue hero will be standing right at your gates, and the Purple hero will be nearby on the road to the Dungeon.
4. I had a fortress even with a capitol. I tried waiting for additional troops to be born in my fortress, but it didn't work; they called for reinforcements, and that was the end. I came to the conclusion that I should buy as many troops as I could in my fortress, abandon it with the capitol, which was built up to the dragon stage, and go to the Dungeon.
5. The Blue hero immediately took my fortress for free, without a fight. The Purple hero wouldn't let me into the Dungeon. I had to go around him on a different, longer road. I went into the Dungeon, broke through the gates, and then I met two more Purple heroes along the way; I also let those fools go up, let them fight with the Blue heroes. I have a lot to do down here. Several days passed, and I was without any fortresses at all.
6. In short, while the Red and Purple heroes were killing each other with the Blue hero, I took all three Dark Elf fortresses and held them for more than a week.
The Red hero tried to go down, but I stood on the bypass road behind the fortresses in the middle, and my logistics didn't allow the Red hero to go down; I would have killed him, and he ran back up again.
7. I bought an army and went up. Everything else was a matter of course. I have 3 fortresses, and they have 3, but they have to share them among three.
In short, I killed them all.
8. I used "quick battle" everywhere. Logistics were maxed out. I didn't level up magic; I leveled up combat skills.
9. The difficulty of the scenario is that the Red and Purple heroes are ALLIES; you can't turn them against each other. But you can turn them against the Blue hero, which is what I did.
In short, it's a great scenario. Lots of fun to play.