Your strategy for playing as Necropolis.

I don't consider Undead a significant unit; it takes too long to get them, and Vampires are more effective and faster. I'd add Archers, Zombies, Vampires, and Liches – that's the whole striking force (though you need to consider the timing).

Undead are actually good creatures, and you should unlock them as early as possible. Dragons are the strongest undead units, the weakest among the seven, but still quite strong, and dragons with vampirism can compete with all the others. So, my tactic for playing as Necropolis is to unlock Undead and Dragons as quickly as possible.