Auto-translated
Hmm, I completed this mission using a hero. Before this, I hadn't played Warlords of the Horde (only the prologue campaign, of course), and I've only played Heroes 5 about 10 times, and only in PvP. But I've been playing Heroes 3 since the release of the Armageddon's Blade expansion, about twice a week (PvP). Getting back to the point: the mission was completed relatively easily:
1. Test run. Just reviewing the map, marking points (I always look at the map first). The AI defeated me quite easily – on the fourth week, after visiting the witch.
2. The actual game:
I reached the first Castle without losing a single unit in any battle. I didn't touch the manticore or the archers guarding the pile of gold. I took the Castle, preserving all the vampires (22 units) and 12 zombies (I replayed it about 7 times to find the tactically correct formation). After that, with the support of the vampires, I raided the mines. By the end of the 4th week, I took the Mountain Fortress (all the dwellings in the Castle were built, but not upgraded (because it's not allowed) by the middle of the third week). By the end of the 2nd month, the Red Castle fell; it didn't cause any particular problems because, on the 5th week, I approached its Castle with such a force that it couldn't take the Castle, and it couldn't defeat me in the field. I set up a blockade, positioning myself right next to the Castle. As a result, I received reinforcements from my home Castle (three heroes specifically purchased, and reinforcements only take one day, the first DD), and from all available dwellings, while it just sat there, afraid to come out. The main striking force in that battle was one and a half hundred High Vampires (I resurrected a lot of them, and I had a good number of my own). And the AI took the Green Castle on auto-battle with almost no losses on the 6th day of the 4th week of the 3rd month. There you go!)