Demon invasion.

you need to break through to the castle in the bottom right corner as quickly as possible. even if there are difficult neutral creatures there, you can ignore the losses. build 1-4 creatures and a castle in that location and in the starting castle; it doesn't matter if you focus on Knights and Lords. by the time the first wave arrived, I had around 400 Imps, 400+ Demons, about 200 Hellhounds, 80+ Succubi, and a few Knights. level 20, with Dispersion and Berserk, but no Slow. I won, with losses of 250 Imps, a couple of dozen Hellhounds, and I had to sacrifice some Knights. I even found a screenshot - https://i.imgur.com/tXdZS4Y.jpg