"Low frequencies, Princess," he said. Celestia looked puzzled, and he explained, "The fae sprites. I... investigated the weapons the humans produced to counter my sprites. The others may work as well, I don't know, I'm not familiar with all of their technologies. But the only one that I know for certain would work is the sonic cannon, if set to ultra-low frequencies. I'm... not certain exactly what frequency would work best, the humans will have to figure that out, but it will drive the sprites back, hurt and confuse them." 