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Battle Mage. Why? Because there's nothing worse than a mage who can't be killed, either in melee or with magic. Of course, if possible, I'll cast another spell on him, but I always choose Battle Mage. Without hesitation. And I try to upgrade anti-magic to at least 50%. As a result, you get a kind of universal fighter, like a barbarian, but with skills developed in reverse order. That is, you can take a barbarian, fully upgrade his Battle Mage skill, and then what? You need to take some magic skill. But here, it's the other way around: first, you upgrade magic, then Battle Mage – the result is identical because, in essence, there's no difference between the heroes, only the images (faces) are different, and barbarians don't get any additional bonuses just because they come from a "barbarian" city, right? Similarly, a mage doesn't get any bonuses to his magic, so you can freely customize heroes as you like. No matter how strong your mage is, without magic defense, another mage or a stack of magic creatures will always have the opportunity to defeat him. And what's most important in Heroes of Might and Magic IV? The main thing is to kill the enemy hero first, and that's it. The battle is practically over at that point; no hero, no army. The enemy hero is always (in 95-99% of cases) target number one. Therefore, you need to take care of your own defense. What do I care about these +20% to illusions, -2 mana per spell, if my mage is lying dead at the feet of some miserable bunch of vampires? Let my mage consume more mana, let his arsenal of spells be more limited, but they will be guaranteed to work! And I will definitely cast Berserk or Hypnosis on you, and I will certainly try to make sure that after that, your army has one less hero. In general, in the army, you should also have another mage with infinitely useful spells for maintaining order – "Martyr" and "Magic Bolt." Fortunately, these are only level 2 spells from the Life and Chaos schools.