anti-Necropolis faction

I used to think the same way... But no, that's not quite right. You need to suppress both the summoning and the creature itself. Otherwise, you'll face a serious problem. And you'll get elementals (if you're lucky, not fire elementals)... And a decent amount of undead will be raised. So, the best counter to Necropolis is either Haven or Inferno, I think everyone will understand why. Especially why Inferno.