What skills should Necromancers take when facing Orcs on a very large map?

Light might be problematic, as it drops very rarely (2%), so it's not reliable. Chaos, on the other hand, is quite good; with a large amount of necromancer magic, the damage will be significant (not as good as a Warlock with Arcane Wave, but still great). However, darkness is indeed the most useful, especially against Orcs, and not just when playing as Necropolis.