New order.

The main striking force was the mages. Three Castles with a bunch of outposts and the ability to quickly place the Tear of Ashera (I had it on the surface, next to the second Academy Castle) leaves no doubt as to who is in charge. The demon was listlessly digging around in the basement. An army for him was gathered slowly, resources were spent on building the magic Castle. The biggest difficulty was that the Academy units don't want to move quickly. For most of the game, I was searching for where that Faiz was hiding.

Regarding the Throne of Elements. I cleared the map with almost the starting army. I captured all the Orc Castles and the blue Castle. When I reached the Elves, my largest stack consisted of about fifteen Adepts (without griffins, unicorns, and seraphs). All of this was easily defeated by three tiers of Necromancer units. Then, before finishing the map, I visited him with the final army just to see what would happen... It turned out that nothing would happen - just an addition to the army, which was already huge. I missed out on troops more because I couldn't train in two Castles at the same time.

For this, you just need to know that it is a bug, and not the author's intention. And the shamanic ritual with reloading the game didn't work for me either; the heroes didn't appear in the tavern.