Well, after many attempts, I finally found a strategy to complete the map. The hero must destroy the garrison, visit the brown tent, and immediately run southeast to liberate the town as part of the quest. And around the town and in the surrounding areas, there are hordes of monsters, all of which join the hero. About 1,500 zombies, assassins, vampires, etc. I even managed to recruit 60 phoenixes a little later. And that's it. After that, it's smooth sailing. We block the gates in both dungeons, resolve all issues on the surface, and then go down. Although, I went down, but haven't had time to explore it yet.
OK, I wandered around, escaped, reached the quest castle, took it, and started looking for who would join me. Aha, besides the 60 fairies near the castle, everyone else wanted to fight...