Rock of Grimheim

"Grandmaster-level tactics" are present here, referred to as the "trial and error method." The AI heroes have very different skill builds and behaviors. You need to try different strategies, different builds, and different army compositions (more than 50 dwarven dragons, which can be recruited from both castles, helped me a lot in the last battle). The AI is strong, but not invincible; sooner or later, you will find the right tactic and defeat even the monsters from the later waves. Yes, randomness will make the task more difficult, and your "archery range" might get very hot, but the feeling of victory, knowing that you managed to outplay them, is worth it.