You could take Hold The Line or Prized Sorcery as you have 2 wizards in your list (Nagash and Mr. Kainan).
I think Mr. Kainan could work, stat wise he is really good value to me. His ability Executioner’s Strike is pretty sick. Don't forget that his keyword is Mortis Praetorians though, so he doesn't benefit from Petrifex worsening rend or improving rend from bludgeon.