Various methods for neutralizing skeleton archers were discussed here, which is, of course, vital against Necropolis. So, Slow and Mass Slow are often found on Necropolis heroes, even more frequently than on others, and skeletons don't always stand in one group. And it can be difficult against a good Dungeon hero. You need to try to obtain Remove Curse or acquire amulets against Distractive Magic as a backup. In general, it can be very important which hero goes first.