Sylvan vs. Necropolis

You could try focusing on Blood Dragons, Dragons, and Vampires first, then start dealing with Skeletons, Ghosts, and Liches, and at some point, use the Enchanted Arrow of Vengeance to unleash a rain of arrows. The downside to this strategy is that the Vengeance skill seems to be only useful for making the triple Vengeance attack a rain of arrows. However, completely eliminating Dragons, Blood Dragons, and Vampires might be worth it? I haven't tested this yet; it's just one of those crazy ideas, and it might be very foolish.