Odd, isn't it, that Darkness is opaque to Darkvision? Especially since there's already a Deeper Darkness spell out there. Anyway, an epic Twilight spell makes perfect sense.use a darkness generating spell that does allow darkvision, maybe something epic with a very large area of effect.
With that in mind, perhaps we should arm our Darkvision troops primarily with missile weapons.
Unfortunately, the Valloreans have started their military campaign in spring. I doubt we can delay them until winter. Maybe some epic magic can change that.Fighting in winter when its very cold is an advantage for the undeads not to be underestimated (see WW2)