Found a bug that allows you to complete the main objective: gather 700 archers (still figuring out how it works).
While playing as Necropolis, I started splitting the archers (outside of battle). I had 521 of them, and when I finished, the game registered my victory.
Мой канал по King's Bounty - "Remix Play"
Моя группа по героям 5 - Здесь отвечу быстрее