Demon invasion.

It's more than just difficult. I started on Veteran difficulty. I cleared the surrounding area with almost no losses (except for the Titans). A yellow hero of level 24 emerged with an army including fully upgraded Devils, while my maximum unit was just Knights. I would have had a chance to defeat him if it weren't for his well-developed Chaos magic with Meteor Shower. It's almost pointless to level up magic skills myself; after 20 levels, you only get 3 spells, which is ridiculous, and trying to get a hundred Druids just to get a staff... that's not ideal. And the inability to build a Guild higher than level 3 and a Castle also isn't very encouraging. After many reloads, I managed to create a situation where the yellow hero ignored me and killed the blue and green heroes. I managed to gather a more or less decent army, but I still don't have a chance, thankfully, he doesn't attack unless I move to the crossroads. In my opinion, the damage from skills needs to be increased; otherwise, you simply don't have time to develop properly before the enemy activity starts.