After Fluttershy's loving spirit leads her to attempt to treat a bear infected with rabies, she is wounded to a point of no recovery. Angel Bunny found Twilight in her library and took her to Fluttershy, but Twilight was unable to heal her with her magic, and she was losing blood too quickly; she acted with what was her only chance: using Alicorn magic, the same dark energy that corrupted and consumed the normal unicorn King Sombra. The dark magic saved her, and with no side effects to Fluttershy. However, Twilight was driven to delve more into this sinister force that managed to save her friend and do what normal magic could not, once again. The taint of the magic began to seep into her, causing her to shun all normal magic and cast spells that were forbidden to use. Spike saw this unfolding and went to ask for help, but his pleas fell on deaf ears, as he was dismissed as being paranoid every time. He could not bring himself to return to her in that terrible state, so he left Ponyville in search of anypony who could convince her to give up the Alicorn magic before it was too late; little did Spike know, it was already far too late.
