Developing a Necromancer hero.

A small clarification regarding summoning and mines... this will allow us to rush on small maps, just like Kaspar.

Leadership, magic – forget about it...

Education, if you plan to play a game that lasts 15+ turns.

And if you're playing against someone you know or against a Human, you can take Light and Mass Dispel because mass slow against Undead is deadly.

Chaos, together with the Lord of Cold, should be taken on small maps when rushing or in a not-too-long game of 12-15 turns, if you see an Ice Elemental in the guild, and there's a +50% cold damage amulet on the map.

Luck, if you have a free slot. Deadly Luck only if you have artifacts with similar effects and your opponent is playing WITHOUT Luck, because a simple -1 is nonsense. And against an Elf with 5+ Luck, it's completely useless.

Logistics depends on the map. For example, on the Wastes, the entire land has no penalties for Undead, so a Ranger is not needed, and losing levels on a small map is deadly.

Battle Machines are a must for Kaspar (and he should have the Plague Tent and Ballista if fighting in the field, and the Catapult if given right before a siege), and for the others, it depends on their play style and how much they like this skill.

But personally, I prefer the option with Master of Mind, Master of Curse, and Spirit Link. In my opinion, mass slow and dispel are more useful than Cursed Lands. For example, they can be obtained very quickly, and then battles with many neutral creatures become much easier, and most ranged units turn into mincemeat in any quantity.

I agree, the only exception is if there's already Plague in the castle guild and the opponent has many low-health creatures, then take Lord of Pain. This advice also applies if the hero doesn't have Darkness at the beginning, otherwise, the skill can wait if the heroes' levels won't be very high.

Defense, if against magic, take Resistance; if against ranged units, take Dodge.

Attack is almost mandatory...

P.S. Oh yes, and I almost forgot... Banshee's Wail is nonsense, IMO. -1 morale is the same as Deadly Luck, and losing -10% initiative is, of course, not bad, but when the hero has few levels, you don't want to waste an extra skill point on it...