Walkthroughs for custom maps.

Perhaps I won't delve into that. Maybe it would help to reduce the Lich's defense to 0 with a destructive beam and then attack with a stack of demons with a fire shield applied? Or use the fire shield counterattack of the Ifrit Sultans (if they are even on the map). And replenish losses with cloned Archangels. Perhaps the author actually has some plan? I just checked the author's description attached to the archive, but it contains almost no clues and says nothing about the final battle. Maybe something was said about it in the map's events?
The map author is Hans C., who also created "The Lone Knight" and "The Uprising." I completed the first one (the report is published here), and I plan to play the second.

You can't reduce the enemy Lich's defense to 0 because with the sniper bow, they simply shoot down our army: 32.5k damage in 2 shots kills any of our stacks (except for demons). We won't have time to reduce their defense, and we don't need to. Just attack them with demons while they are praying and support them from behind with Phoenixes so that the demons aren't attacked by everyone. The rest of the army can simply be sacrificed; the demons will finish everyone off. Losses don't matter because this is the final battle. In general, the battle is drawn out. I don't remember any hints from the author on the map; it was a year ago. As far as I remember, the map is very good and passable, but there are a couple of difficult spots: how to get through the first week, how to reach the angel castles, how to kill the hero with black dragons in the underground, as well as the water battle (I think it's against Medusa) with the Phoenix sacrifice trick and mass blindness (!), and the final battle. There are hints for all these moments on maps4heroes.com.
I haven't played "The Lone Knight," but I did play "The Uprising."