“Ashes’ Will” – “A Sad Journey” [Campaign 2, Mission 2]

I don't quite agree that 3 schools of magic are too many for a Necromancer. In this Campaign, we are playing against heroes who are very skilled in Chaos magic – mages and demons, so my primary goal was to weaken the enemy's magical attacks as much as possible. Here's how you can develop your character effectively: take Defense, level up the Reflection perk (-15% of enemy magical attacks), then take Enchantment, level up to "Arcane Knowledge" and get the Undead Protection from Magic perk, which is another -20% of enemy magical attacks. And that's where Chaos magic comes in handy; level up to Storm Lord and get the Magic Drain perk, which is another -20% of magical attacks. In total, we get 55% less damage from any offensive magic, so choke on your wand, you lousy mage! :D
P.S. Alternate-gray skeletons, by the way, have 25% magic resistance, so with all these perks, the skeletons become almost as tough as golems, which are completely immune to magic