Warhammer world is a cruel and a crazy one full of monsters yet why are the battles predictable? Where most people play SP the campaign needs a third party spawning during land battles like in the quest ones (put approx 5% chance of spawning one).
Think of wandering raiding party (orcs, beastmen) Joining the massacre! Skaven, WE putting ambushes to finish of the survivors. Or just harpies/monsters smelling the bloodshed. What do you think?