Necropolis – a triumph or a failure?

Is that not enough? If even half of the mines explode, that would be good. And if 3 of them are wasted, what's the point? Besides, their damage is comparable to that of a first-level skeleton. And if vampires or shields are active on the dragons, they won't even care. No, if you're going to cast spells, it's better to use Armageddon or Darkness; your minefields are only good for clearing out neutral creatures.