Demon invasion.

I acted this way in the second game. I, of course, recruited Nimues. In the cities, I built gold mines first, and then a building that gives +10% to the gate, as soon as possible, regardless of losses. I broke through a one-way portal near the castle that leads to the lower right castle – there’s easier prey for leveling up, plus a couple of dwellings. Before the first enemy arrives, the main thing is to build the castle + 1-4 upgrades + a guild to at least level 4 in the first and lower right cities; you can ignore the other cities and upgrades. I got to level 20+, with stats like: logs/darkness/luck/attack/defense. On the previous page, I posted a screenshot of a battle with the first enemy after such preparation - https://imgur.com/tXdZS4Y. And after that, there are no problems.

And there’s a feature in the Shio campaign with the heroes. Near the top city, there’s a two-way portal – if you enter it, the enemies won’t follow you past Sigrif, and you can sit behind it, calling in reinforcements from the cities above, and at the beginning of the week, intercept the enemy’s castle, take the increase, and go back through the portal. This is how I accumulated troops, and then I easily defeated both demons in the dark castle. Here’s a battle with Grok that I found -

I built the 10% summoning building quite quickly.
But there’s a problem with combat buildings; if there’s an ore mine, there’s no wood. Wolves can’t be killed right away. You build imps and unupgraded demons, and that’s all. With these imps, unupgraded demons, and random troops from the refugee camp, you can’t kill many. I have problems with the hero precisely because of the lack of combat buildings and the ability to build them, while the average neutral army is a level 4 creature. You spend a week gathering troops, and you always max out the stats, sacrificing 1 imp at the altar for 2 luck, and that’s all it takes to have 1-2 battles per week with a good percentage of losses (the losses are small in themselves, but large in terms of the percentage of losses, even for the same ore mine). If you’re lucky with the ballista, it’s okay, but if not.

Near the second castle, all the ranged units shoot, especially the elves on the way to it; you can’t get there without leveling up.

That portal was guarded by 500+ manticores; I wouldn’t have passed them even if the author hadn’t made them level 7 undead with a small set of spells, but if they were the same useless creatures, you still couldn’t pass them :) you could only hide in your necropolis city.

I passed the Death Knights because of the narrow passage with the crystal of secrets.