Reverse engineering
It would be cool if when a creature gets a weapon that they can't normally make (shotgun, laser gun, evil + good mage staff) They could reverse engineer it and make it a mass-produced weapon, Here's an example:
Before a laser gun was reverse-engineered
After (They all have laser guns now)
This would be cool if you wanted more "modern" warfare where attacking armies have guns and stuff instead of swords and bows