Yuri_G
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I'm planning to do roughly the same thing, if I can defeat the last demon. I think I can, because Railag already has a sizable army, including black dragons. I'm keeping a large army in the frontline city, led by Shadia. When I went to the teleport near the second city, she was guarding the first city. Now Railag has gone to the teleport near the first city - I moved Shadia to the fourth city. Reinforcements are coming to Railag from the first city, and to Shadia from the third.
I didn't know about the ground part, but I'll still find it, because I'm going to explore the entire map. If all goes well, one hero with a very strong army will stand guard near the last city and won't let anyone out, while the other will calmly explore the territory. Then they will switch.
I've completed this mission and understand which castles you're referring to (or rather, I can guess based on the numbers), but if someone tries to follow your path, they might get confused. :)
Apologies for the off-topic comment.