Worshipper – “Ship” [Campaign 2, Mission 4]

I'm replaying the campaign and just finished this mission yesterday. The hero uses Chaos magic. First, I take the Demon city, then the Lower Elves, the Right Elves within the first month, and the Left Elves in the first week. After that, you can accumulate as many troops as you want because the last castle won't go anywhere, and the garrisons in front of it won't increase. You just need to create a mix of troops. I had around 40-60 Elven Archers as the main force and about five Treants from Inferno, 9 Nightmares, 12 Cave Lords, and 10 Cerberuses. That's enough to easily defeat the Elf with a reserve.