I finished the game after saving and taking a two-week break.
I got lucky and spotted the opponent's outpost, which gave me information about his approximate location. I saw him heading towards the treasure, and based on the two Necromancer heroes, I knew there would be a lot of skeletons. I started gathering Wyverns, upgraded them, and headed for the treasure. The captured Companion Tower with its scouting ability also allowed me to see adjacent areas. In the treasure, I took a few hives, and each objective was a tough fight, resulting in some losses. As a result, after 100+ turns with Gorgons, I saw the opponent's Castle. I had time to think, but without slow, I managed to defend the Book of Earth, losing 15 Wyverns and half of my Bulls.
I tried to regain my strength by gathering resources from the previously scouted mines during the first two weeks, but I didn't take them before the treasure because they were all level 3-4. I captured the purple swamp.
By this point, the opponent was emerging from the treasure and heading towards my main castle. He had a legion of skeletons, 15 Phoenixes, and a large army; his combat stats were higher, but his magic power was lower. Alkin teleported to the castle, having 16 Angels, some Cows, 40 Monarchs, about two weeks' worth of troops, and Spell Power 27. The explosion power was roughly equal due to the opponent having the Sphere of Earth, which was disappointing. I cast an explosion on the skeletons, received Monarchs in return, and 15 Phoenixes finished them off. At the beginning of the round, the explosion cost me 16 Angels. I was thinking about how to resurrect them when I saw a ransom offer for around 100,000!
On my turn, I took the Utopia with the Chieftain, which I desperately needed, and then I went to take another Utopia that I had scouted earlier, after which I saved the game.
I saw where the opponent was going and that his army was divided. I could have reached the opponent's hero guarding the skeletons and the main castle without skeletons, but I couldn't find any Amulets of Protection, either in the castle, on the black market, or on the map.
With Alkin, I took the Utopias, found two Red Spheres, and only needed a Shield to complete the set for the Angels; the hero grew noticeably, and with Earth and Logistics, he gathered resources. I gathered all my troops, having 70 Monarchs, a solid army with 28 upgraded Unicorns, and attacked the opponent in the castle with 2600+ skeletons, 21 Phoenixes, 11 Angels, 113 Storms, 45 Vivs, Magmas, and Psychics. The advantage in stats was now clearly in my favor, and I was wearing the Amulet of Protection.
I defeated the Monarchs, flying around, and the Phoenixes and Angels, losing 13 of them. The opponent started bringing out skeletons, guarded only by Vivs, Psychics, and Magmas. In the next turn, only skeletons remained; after attacking the Hydras and destroying 8 of them, the opponent surrendered.
Thank you for the game!
I haven't seen so many skeletons in my games before.