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I completed it on a difficult setting. I played as a Wizard. The best units are Liches and Spider Queens in ranged form; they deal the most damage. My tactic was as follows: first, go to the left, take the Fortress, destroy the Dungeon, and then proceed to the Castle on the surface. Take the Castle, build structures that slow down approaching enemies, and, of course, build portals. Next, destroy the Dungeon from above; I couldn't take the lower one without losses, so I teleported to the main Castle and pushed north. There, again, is a Fortress, a Castle in the Shio region, a Castle on top, and a Castle in the Shio region. Occasionally, a hero from the lower Dungeon would raid the westernmost Castle. Don't forget that we have a "slow" structure in our Castle. Wait for him to get closer, teleport to the Castle, kill him, and teleport back. Then, I collected the Tears of Ash (one piece above the western Castle, one on an island in the sea below it, one in the desert near the northern Castle, and one near the northern Fortress, i.e., all nearby). I built it, and after that, the most difficult part was taking the lower Castle in the Shio region, but even that can be done without losses if you try. With three Castles and the Tears, I think everyone can manage.