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Good scenario, I enjoyed it.
The first time I tried to get Sandro's cloak, I was very surprised by what was inside and how difficult it was. So, after building up my army and buffs (I ended up with 5 Spirits, +13 Luck, and +10% health from map enhancements), with the stats/equipment shown here (
http://c2n.me/3RNKo9T), skills (
https://c2n.me/3RNKEfU), and army (
http://c2n.me/3RNKVNd), I faced this battle (
http://c2n.me/3RNK9dV), in which my archers were somehow recolored. Even though I had a bow equipped, I only lost 1 attack. A Phantom would have helped in the final battle, but I forgot to learn it in the towns. Any spell cast for mana would have been countered by Naadir's counterspell (I chose Summoning for balance and Banishment), but I still won without the Phantom. I thought that since the hero was under a permanent counterspell, the creatures would be too, but they cast spells normally.
In the first battle, with the Ring of the Magi, the catapult managed to destroy two towers in the first turn.
At the beginning, I almost lost. Once, after two attacks, I survived with only 5 peasants (not single units, but in one slot, in a battle with full armies).
Regarding levels, I don't know. I took 10 Defense, which seems more useful than 2 stats per level and 2 skills for "filling in the remaining slots." I had 1 empty slot - Experienced Commander, which is useless in battle = 0