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I will try to answer all questions as best as I can:
1. A map similar to the Dragon Pass, with two Castles for each player (one of which needs to be taken from the AI Hero), and two Dragon Caves. Under these conditions, the chance of gaining Vampirism is very high.
2. The opponent is most likely Laslo, any Orc (it would be bad if it's Haghesh) or a Demon (which would be bad because of the large number of Imps), or perhaps an Elf. Definitely not a Warlock, Mage, Necromancer, or Dwarf; my opponent doesn't like to play or is not good at playing them.
3. The game is in the late stage, 30+ levels. At these levels, I don't consider Chaos Magic to be a problem. By that time, I will have around 500 Inquisitors, which is 41k HP. So, who cares if someone hits me for 1k HP with Chaos Magic?
4. I take two magic skills for variety. Twilight + Fallen Knight already gives +8 to Spell Power. If necessary, I can control with Darkness and remove control with Light. Plus, mass spells are not very demanding in terms of Spell Power. Also, the weakening attack (preventing the hero from attacking) from Guardian.
Leadership, I also wanted to take, even though my main stack will not be undead, but I have two strong stacks, and Empathy and Inspiration for the Inquisitors won't hurt. Plus, if Readiness isn't useful, then it makes sense to take Battle Fury and go for the ultimate ability "Unrelenting Force." I wouldn't replace Leadership, as there is a Mentor on the map, and over time, I might replace Luck with Education or Attack.
5. Initially, I will fight offensively. I don't need "Tactics" for defense because, with this many Inquisitors and Griffins, I can easily defeat any ranged stack. And in the end, when there are still a lot of Inquisitors and Griffins left on the battlefield (it's not very pleasant to fight them, with Battle Fury, Endless Retribution, and Guardian with Weakness), I will take a defensive position.
6. I disagree with the opinion that Iris is less useful than Laslo with only one Castle. Under Laslo, the best stack in the game is the Armored with retraining, but there is only one of them, and they have low initiative. I will have two mobile, semi-strong stacks that can be considered as one strong stack (a lot of Inquisitors and a few, but strong in stats, Griffins). Axel + Paladins is a disaster for the economy; it's too expensive. Inquisitors are a great budget option; their HP is not inferior to Paladins, their damage is much lower, but they shoot, and they also remove positive effects from the attack (with this many Inquisitors, they will remove it with a probability of 60-90%). Iris easily gets Luck of the Draw and Treasures, and she has the least problems with gold compared to other human heroes. 40 Inquisitors will be enough without any loss to the economy.
7. Regarding magic control against the opponent, I believe that Haven is the most protected Castle against Dark Magic in the game. Paladins, Inquisitors (80% chance of removal), and the hero himself – that's already three stacks that can remove control!
8. Regarding Readiness, thank you, I didn't know that it only applies to one attack. Then, instead of it, it is worth taking "Battle Fury" and possibly going for the central Haven ability "Unrelenting Force" and applying it to Griffins or Inquisitors. That would be even better. With Dark Magic and a weakening attack, the effect will be excellent!
Perhaps the hero will not be as versatile as Laslo and Axel, but he can definitely compete with Dugald and Myv. If I missed something, I will add it later.
And one more question. Doesn't the removal of control with Cleansing or Antimagic depend on the difference in Spell Power? (Total dispel chance = base% + (Dispeller_Level - Caster_Level) * 3%
Level of creatures is 1-7 for normal, and 2-8 for upgraded creatures.) And I thought that Spell Power affects the chance of removing, for example, Haste over Slow, etc. That is, I think that with a skilled Light Magic, I can remove control with 100% chance, regardless of the opponent's Spell Power.