Oh, how helpful defense is! For the Necropolis, it's the second most important stat after magic power. Without it, the chances are very slim. I can confirm this. I attacked Godric with Markel, first using a strategy that emphasized defense, and then we tried again without it. The damage of the Knight units increased by approximately one and a half times, and I lost without a chance. Then, there's resilience – warrior skeletons receive a +33% bonus to health, considering that they are always the main attacking force.

And teleportation is certainly difficult – you either need to level up another hero and give them education with the ability to learn spells + light magic, or have the same demon or warlock level up their education as well.