In the second game, the natural enemies of Necropolis were Sorceresses with Elves and Phoenixes, as well as Knights for certain reasons. I think that the strongest in this trio are the Elementals. They have three arguments: in the first stage - upgraded fairies, then - storm elementals, and in the final stage - the number of phoenixes and the magic university. Mages are very dependent on the map (in particular, the presence of leprechaun gardens and what they give). Necropolis is very strong, that's a fact, but it can fail against Elementals - vampire lords are not that strong, and there are traditional advantages of the Conflux.