In a darkened forest, a cult attempted to bring the spirit of King Sombra back to life. Their goal; imbue the spirit of King Sombra with far more dark magic than he ever had, and take over Equestria. When Twilight Sparkle intervenes, things go wrong, and something else is summoned. Something that Twilight is familiar with, and hoped to never have to deal with again.

Something that may not be worse than King Sombra taking over Equestria.

Something far, far more obnoxious.