Tactics against Necromancers.

If you have a higher level and more troops, you can defeat anyone. But what if you're weaker than your opponent in every way? If the Necropolis faction is very strong (both the hero and the army), you can only fight them with powerful magic. Or with high-level dragons. Also, the Tower and the Conflux are powerful. And hydras can easily overwhelm skeletons with sheer numbers.