Tactical techniques for conducting battles in Heroes of Might and Magic II.

Yes, in online games, especially on small maps, Necropolis is one of the strongest factions, only Warlocks can defeat them...

That's a bit too categorical :) "Only Warlocks" (with a wink).
What about Knights? They have a bonus – double damage against undead!

As has been said many times, it all depends on the specific situation.