Would it be extremely difficult to add a few “Lovecraftian” banners to an existing Medieval army, to make them look like the pro-“invader” faction? Would banners alone do it, with some creatures sprinkled here and there?
And perhaps make a portal for “eldritch” reinforcements?

I’m hoping for some versatility for my existing human force and not a complete overhaul and repainting of the entire army.
Thoughts?
Dan