Tactics for Necropolis.

I have another question for the esteemed experts. How can you survive on an XL map with a Dungeon faction against Necropolis? Please don't suggest playing as Necropolis.

P.S.: The opponent also knows about Dragon Utopias, Books of Magic, Wings, etc.

Does he just know about them, or is he a pro at playing Necropolis? If the map is random, there's a very high chance that Necropolis will get a starting location in the Dungeon.
(I have the complete collection of Heroes 3, and in that version, Necropolis starts in the Dungeon 90% of the time on a random map; I don't remember how it is in SoD.)
Starting in the Dungeon with strong monsters should slow down their development by 200% (in theory, with equal skill levels), due to narrow passages, inconvenient locations, etc.
What are the rules? Are Warlords, teleportation magic, and diplomacy allowed?
If everything is allowed, you can try to reach him quickly before he gathers a huge number of skeletons. If that doesn't work, you can try to gather Dragon Utopias and find a vulnerability sphere (blindness, berserk).
And then, into battle!:smile13:
And as people correctly advise, use more mage heroes: attack and retreat. As an option, play Dungeon (although you might also start in the Dungeon): Armageddon should appear on such a map: attack with one dragon, hit, and run away. Good luck!