Wave after wave they came. Day and night the air echoed with the chorus of their distant honks. The sky was filled with them, coming at us in V-formations. Half a mile up. None of our weapons could come near them. If they had come down to our level, and fought like a duck .. but oh no, they just stayed up there and passed over.
Each duck had swallowed a few dense stones which they spat out as they flew above our position. They had surprisingly good aim. After releasing their load, they just circled back home. Probably bobbed around in a lake and ate more greens for awhile, loaded up with more stones, then made another go of it.
A typical one-ounce stone would hit at 150 miles per hour. Castle walls? No protection at all. Inside and outside were equally exposed to the sky. A single stone could kill anyone out in the open, or put a good dent in any roof. Days of waves had demolished every roof. The surviving structures were massive stone walls. No matter what their original purpose was, those walls were now of no use to anyone. The surviving army was holed up in old mines.
We didn't know how the Dark Lord controlled them. How do you pay a duck? Maybe he had a tremendous supply of bread? Maybe he tortured foxes for their entertainment? For all we knew, he was just really good at quacking.
Signals said the Dark Lord's regular forces were roaming freely across the land, pressing his thumb down on villages. Having their way. If a village objected they got the duck treatment. Nothing we could do about it. Leaving the mines was suicide. Staying in the mines ...
We had prepared for armies. Archers. War machines. Traitors in our ranks. But not ducks. It was just a matter of time before we ran out of food. Just a matter of time.
This was in response to a prompt on reddit.com r/WritingPrompts, "The forces of good are currently in trouble due to an attack by the Dark Lord and his army of.... ducks."