Everything!
Yesterday, I finally gathered my willpower and completed this map. The presence of archangels, fanatics, stormbirds, and vampires in the final battle was a given. However, I experimented with the remaining three army stacks. While building my army, I used Dess to explore the dungeon and bombard neutral units with the King of the Dead's cloak. I encountered packs of 4,000 wolf riders and griffons. In this way, I raised my skeleton count to almost 30,000. I also decided to include ghost dragons and black knights in the army. First, I waited in front of the castle to accumulate mana. Then, I paid a visit to Deemer for a cup of tea. He didn't put up much of a fight: mass slow (on me) and mass player (on him), his shooters with spitting attacks kill my fanatics (there were about 4,000), and he stays in the castle. My skeletons and black knights act as spectators. Damn! I need to change something!
I decided to add archers and good flying units to the army. For the black dragons, I took titans (there was an option to take liches, since there are twice as many Necropolises as Towers + a cloud of smite could affect three units at once). And to quickly remove the initial effects, I took golden dragons, due to their immunity and high speed. I waited a long time to accumulate enough money to buy the entire army. In the end, the army composition turned out to be: 1200 golden dragons, 800 titans, 800 archangels, 800 ghost dragons, 7,000 stormbirds, 7,000 fanatics, 7,000 vampires (I'm writing this from memory, I might be wrong). I equipped items that give +morale, +speed, an artifact that "disables" luck, accumulated 8 mana (4 restored per day), and went into battle. As expected: I removed the initial buffs with mass dispel in the turn of the golden dragons. I attacked the medusas and harpies with them; in response, the enemy's infantry took them down. Manticores flew at the fanatics - they were quickly defeated. In the end, everything was going towards my victory, if I hadn't overlooked the fact that I was standing on dead earth (I can't cast spells above level 1), while the enemy could. He blinded as many as he could - archangels, stormbirds. And then he effectively cast "sacrifice" on the defeated units and restored minotaurs. For the rematch, I accumulated more mana, equipped the "three-liter jar of petroleum jelly" artifact, and went all-in. He defended himself, cast clone on the minotaurs, called his mother for help, displayed messages about a critical Windows error, but he was still defeated. And it couldn't have been any other way.