Walkthroughs for custom maps.

Interesting, does this correspond to the intended author's vision, or is it your own "method" to get through quickly or for some other reason? That is, is it possible to win without "farmed" demons and liches or not?

I am 100% sure it does not correspond to the author's vision! Without liches or demons, I think it's impossible to defeat the final boss (see the screenshots of forces below). EVEN CONSIDERING THAT OUR MAIN HERO Walmary is an armor specialist of level 57!

From memory, the author gives us the Cloak of the Undead King at the very end of the map and, possibly, a necromancer hero (I don't remember exactly if the hero is given or needs to be leveled). On the legion garrisons, you can and should use the Cloak of the Undead King to gather a proportionate number of liches to counter the final boss's liches. That is, this is a very clear indication of how to build an army against the final boss. Without liches, imho, he is unkillable. Thanks to necromancy on a couple of battles, the forces will be roughly comparable to the computer's.
But I broke through those garrisons with some main hero of mine for leveling (I don't remember the exact reason). Later, when I saw the final boss and his 32.5k liches, I realized I had nothing to fight him with and would have to replay all the battles, necro the liches, and go with them. But since using the Cloak of the Undead King on author's maps I consider a rule of bad form (you might as well enter cheat codes for archangel stacks), I decided on principle not to replay the battles with the Cloak of the Undead King. Possibly influenced by AtDandy's walkthrough of Paragon in "no-save" mode, where he demon-farmed several tens of thousands of demons. I decided to use that strategy and also improve the demon-farming skill, resulting in over 32k demons. And even with them, the enemy barely died :)
I'm attaching a miraculously preserved screenshot of the results of that battle, it was quite impressive back then. Appreciate the size of the enemy's forces. I also remember he had some kind of sniper's bow and a couple of other "bad" artifacts for us. Also a screenshot of our forces before the battle. Without liches or demons, 32.5k liches + the rest of the army (and without the Orb of Vulnerability) I don't even know how to kill them :) Whether with Force Field or without, 32.5k liches simply shoot your entire army to pieces. He has the Sniper's Bow, so you can't block the liches.
What's important is that we don't have the Orb of Vulnerability, the liches are not blindable, and Berserk doesn't work! + the opponent has magic resistance.
I found a save before the battle, I'll upload it if needed.