1. Cloak of the Undead King - victory is usually conceded immediately.
2. Skeletons on XL - Mega Power (cannon + Ring of Life = devastation)
3. Vampires and Knights are very good.
4. It's strange that no one mentioned here (or did I miss it?)
the ability to convert Hydras and Dragons into Ghost Dragons.
On my XL maps, I often have no fewer Ghost Dragons than Phoenixes, sometimes even more.
5. In principle, Zombies are sacrificed for Skeletons, and Archangels, Behemoths, Dragons, etc. are taken into the army depending on the situation.
Castle is usually the strongest opponent for the Necro, and a certain percentage of wins is certainly due to them as well. But overall, Necropolis is better.