If you are having trouble with Patrolling monsters continually coming into the heart of your kingdom, destroy one of their nearby lairs. When you are ready, send everyone to the Chalice Site with a huge Attack Flag. Try to avoid Rrongol. One tactic is to use Wind Storm to blow him backward, allowing you to concentrate on the Hidden Chalice Site. If you end up in battle with Rrongol, you are in for quite a fight.
Paladins work particularly well.
You may need to extend Wizards Towers far enough that you can cast Invisibility on your heroes. Regardless, against such a powerful foe, your heroes certainly need a lot of spell support from you. Inc. All rights reserved.