Gantrytor

I played this scenario back in the day. I still remember it. I'm playing on hard difficulty. First, I level up a Knight in Haven. At the beginning of the game, there's a Temple of Magic with regeneration right in front of the garrison. I use it to get 12 Erathian Knights, which we initially have, and we take the first three castles (while on the way, we only level up the Knight to Expert). Nearby, there's a Pyramid with Vampirism (but it's better not to grab it right away, unless you're going straight for Dungeon). When we reach the mentor, we switch the summoning to Dungeon (there's a Book of Dungeon on the map, and it's much more fun and engaging to deal with large groups of creatures with Dungeon). So, we're going for a Haven-Dungeon build. That's it. Whether it's hard or not, the map is easy to beat with a Knight (the only tiring part is grinding through the hordes of enemies). In one of the Warrior's Tombs on the Mage lands, I found the Enlightenment Chainmail. The trick is to capture the first three castles as quickly as possible – the sooner, the better.