Upon being discovered that Twilight Sparkle of Crystal Prep had been unwillingly harvesting magic from the Rainbooms at Canterlot High, the rest of her peers at Crystal Prep decided to seize the opportunity and make her unleash all of that gathered magic against their opponents.
However, magic is an untamable oddity, and when she released it all against the Canterlot High Wondercolts, Twilight became consumed by it and changed drastically.
In more ways than one...