Demon invasion.

I didn't notice that the stats don't decrease when experience is removed, so I replayed and rebuilt the Castle. I cleared the entire island and the lighthouse guards in the sea, gathered a good army from the Castle and dwellings, and upgraded the guild of mages, although I only managed to get the Blindness spell, and the spell on level 5 was just awful. Then I went through the portal, defeated the Hydras and Cyclops without any losses, teleported to the underground, immediately went back up, summoned a ship, and sailed to the purple lands. There, Grobok himself was waiting for me with a medium difficulty level, but due to my specialization, he had no chance of winning, even in his Castle. However, he was losing to me, so I did the following. I took the left Castle of the purple faction; he almost caught up with me. On the next turn, I rushed to the right Castle; he captured the Castle, and I pulled away even further, took the right Castle, grabbed the Amulet of the Blood Claw, which was guarded by angels, and escaped through a two-way portal to the island, and from there to the underground. Keegan chased after me with an army even larger than Grobok's and a huge movement range. While he was catching up, I used 3 movement boosters, defeated the red key master, took out a nearby Krag, and calmly teleported back to my Castle. Meanwhile, the purple faction was defeated because they didn't have a Castle for a week. Only the orange faction remains, but now it has 5 Castles and 2 heroes, each of whom I can't kill yet...