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1. Maybe we'll play sometime.
If you're from Minsk, it's really easy to arrange.
2. I don't understand how you guys reach level 30...
For me, level 20 is already a powerful demon. I can defeat almost everyone, except Wing.
Demons are almost double the army size! Double! You need mass spells; the army will do the rest.
The first three turns of the hero are crucial. The first two turns should be spent on mass spells: Stone Skin and Haste. Everything except the undead will be charmed by the succubus. Given this, what's the point of Darkness, please tell me?
You need defense, attack, and initiative – i.e., Defense, Attack, Luck, and Logistics for fast gating.
That leaves one slot. If the game goes to 30, then we take Darkness for the secondary skill. If it's less, and Leadership is available, I take Leadership and forget about Darkness.
3. About Utopia.
Forget about Utopia for the sake of just two artifacts. In the late game, you can often buy what you need from the merchant.
If needed, you need defense, and on the battlefield, I only deploy devils and imps. Maybe two level 2 units as well.
Keep in mind that I have high defense, luck, and often attack, and I usually already have some artifacts that boost these stats.
In general, in the late game, I move around with a hero who has one empty slot for a unit, waiting for reinforcements, and then I send that joined unit into Utopia first. Otherwise, I don't really go in there...