Shadow sprites. They're known to exist in Equestria, it has been confirmed. However, they despise outsiders with such a passion that not much is known about them beyond that. Nopony knows how they work, why they're such social recluses, as well as what their purpose is.
Twilight Sparkle had made ground-breaking discoveries about these creatures, her notes were found in her journal on the floor of the lab beneath the Golden Oaks library.
Thank you, Flint Sparks, for pre-reading this creepy tale!
Written for the 31shotober challenge!