I'll try another option: move the castle to the underground and initiate a battle with it.
Another option: the hero clicks on the garrison, a script transfers ownership of a pre-prepared arena (a castle with a hero) to the player, and then they can interact with the battle there.
Multiplayer: Господство, Извечное противостояние, Война за Магию, Торговая империя, Анатомия войны, Эксперимент
SingleScenario: Последний Рубеж, Трон, Элиралис, Вернуться домой!, Лабиринты разума
Campaign: Колонизация