The “Maahir’s Gambit” scenario.

It's so strange, the scenario is complex, perhaps the most complex, and there are no walkthroughs. I played all day, there was no logistics, I leveled up the hero to level 15 and ran at full speed, trying to find the Necropolis before it raised thousands of skeletons. I only upgraded Goblins and Mages. I regretted it later and cried into my pillow. So, I found the villain in the tavern; he was weak, but I only killed about two-thirds of his army (damn ghosts, liches, and zombies). So, what and how should I replay it?

Added after 58 seconds
Without Astral, it's completely impossible.