Several days later, in a cavern deep underground, a solemn line of prisoners shuffled to their doom. They were gryphons, wings bound with them chained to each other with a long line of shackles. They were all terrified. Stoic pony guards flanked them on all sides, poking their spears to corral anyone back into line.

And you execute prisoners of war, a violation of the Geneva Convention, had they been convicted of war crimes (which they almost certainly have not). Then I guess it would be ustifiable to execute them humanely. Not via acid bath.