"Give me ten warriors as brave as any,
And I promise to personally bloody as many."
These rare banners from various cultures have in common some kind of inscription in which the holder promises future battle valor in exchange for aid. When the holder says aloud the inscription, they promise to wound in melee as many foes in the upcoming battle as will be granted to them. Then that number of ghostly allies will appear. The warriors will appear and fight as the warriors of the banner's culture, whether bare-chested rhompaia-wielders or mail-wearing knights.
The ghostly warriors can be defeated themselves, but they fight as picked champions. They will fight until all foes are subdued and then disappear. If the oath-maker does not wound as many warriors as were granted, they will age a year for each they are short. So, if they call for ten warriors, they can sit back and let them do the fighting, but after the battle is over, won or lost, they will age ten years.