I saw the best walkthrough somewhere about 8-9 days ago, but I was running out of time...
My result:
15 days
78 skills
254 mercury
696 gold
all castles (there are 7 of them ;))
The walkthrough was simple. The main hero is Kirr (Kair), because his skill tree is very good. I chose the following bonuses:
1) 3 phoenixes - I thought that at least he would have a little more health
2) amulet of divine grace - because it gives +12 to stats, while the sword only gives +9
3) and, accordingly, a cloak of speed
I made a loop with Kirr - upper Necropolis, then the left Ramparts, the green tent, and in the center of the map, I split into 3 heroes, who basically took all the castles. With Kirr, using a portal, I gathered the entire army and teleported to the eastern Necropolis. From there, to the teleport, then to the Dragon, then I joined the dragons, exchanged them in the converter, upgraded them, came back again, and then the scenario was over :). That's the story, friends.
P.S. Thanks again for the tournament!