One day, Twilight comes across a spell that allows one to see across dimensions. She doesn't believe such a silly spell could actually work, but wishes to try it out anyway to see. She uses it on a mirror, and then sees the spell can be set upon a frequency. Out of pure curiosity, she sets the frequency to the lowest frequency the spell has access to: 000.00. She looks into the mirror, to see what this frequency shows her, but sees only darkness beyond the mirror. As she prepares to close the frequency and access another, but then she sees an eye open up on the other side.A black eye.Later in the day, Spike returns home (because Spike is ALWAYS OUT IN A STORY) to find Twilight collapsed on the floor. He rushes to her to see if anything is wrong. He is relieved to see her awaken, but then is beset upon by fear. Twilight's right eye (to him anyways) is outlined by black and the iris has turned red. He relays the problem to her when she's stable enough to get up herself, but when she looks at her face in the mirror, she reports nothing is wrong with her eye, feeling that Spike is just playing tricks on her.As days go by, Twilight's mood begins to worsen, acting out of character, committing to dark magics, and becoming more reclusive then she already is. What could be the cause of this Black Magic?I have no stinking clue because I haven't written it yet