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So, usually, in addition to the basic characteristic – Necromancy (which must be developed immediately), the hero has: Dark and Summoning magic. In Dark magic, we develop 2 options:
1. Cursed Lands, but there will be no mass slow;
2. All mass spells.
Everyone decides for themselves, but it is worth trying the first option, maybe we will reach the Howl, especially if we are not lucky, then we will still come to the second option.
But personally, I prefer the option with Master of Mind, Master of Curse, and Spirit Link. In my opinion, mass slow and confusion are more beneficial than Cursed Lands. For example, they can be obtained very quickly, and then battles with many neutrals become much easier, and most archers turn into minced meat in any quantity.
Summoning, here it seems we either develop Banish, which is not very useful if we are not initially fighting against Necromancers, but it will help against Phantom mages, so I am waiting for your reasoning, I have not encountered this problem, or we develop Summoning itself, but I don't like it, at the beginning, elementals are not bad, but later, with a good army, they don't harmonize well with your green and not very undead creatures.
Attack can only be taken because of Battle Fury and Cold Steel, a good addition to your not small army of skeletons and Co.
Next, Logistics, here there are no comrades in taste and color, if you want to run around the map quickly, take it, but Navigation and Scouting are not needed in my opinion.
Machines, for the sake of the Plague Tent, I think it is reasonable to develop, only for Kaspar, because he already implies it.
Defense, depending on the situation, it would be good to improve to Resistance from the wheel, but not necessarily, the Necromancer's army is not fixated on losses, because it grows and is reborn by attacking its warrior-undead.
Leadership, if possible, it would be nice, Death Messenger with Diplomacy is the best + morale.
Wizardry with Education is not necessary, we can develop without them, and there is enough magic, but I am waiting for suggestions here.