As I understand it, this topic was previously used to discuss any custom maps, not necessarily difficult ones, due to the lack of a more suitable topic. This includes the aforementioned French map, which can only be considered difficult with a very broad interpretation. I suggest trying Limes Inferior at 200%. Compared to it, even Xiedu seems like a walk in the park.
Xiedu and Limes Inferior are simply two different maps. But in each of these maps, you discover something new, even with considerable experience.
I completed Limes Inferior today at 130%. It's difficult, but possible. At 160%, due to the starting limitations, it's VERY difficult, but people have apparently completed it. At 200%, it's TOTALLY impossible. This map is similar to two other difficult ones: Abelia and First Blood. The principle is the same: you either have very little or almost no magic, while your opponents have it. Heroes "arrive" at your location through one-way teleporters, and they choose when to do so. And at the beginning, you have 2 castles, while your opponents have 12 or 7, and it's impossible for you to reach their locations, but they can reach yours. This map is also interesting because it uses very little magic; I didn't even take Wisdom. And you can't learn magic schools, only use the Tazar skill.
And the French map, after gathering some patience, I finally completed it by taking the "long" route. I can say that it's much more interesting that way. With a fast enough pace, you can outpace the author's plan and prevent the apocalypse. You just need to speedrun very well, and you can release all the heroes - the Horsemen of the Apocalypse, i.e., subdue them. With such armies, no one can defeat you