There was no way that Twilight was truly seeing herself in the mirror. She had not succumbed to evil, she knew, therefore she was not a Nightmare. The only explanation was that the image in the mirror was actually a vision of how Rarity was seeing her at that moment.
Long moments passed, in silence. Rarity continued to stare at her, her face still full of hate, though now mixed with a touch of confusion.
"Who the hay are you, anyway?"
Twilight blinked. "What do you mean, who am I? I'm your friend-"
Rarity's response cut off the transformed unicorn mid-sentence. "You are no friend of mine, monster!"
The door slammed shut, and Twilight distinctly heard the sound of a heavy bolt sliding into place. It was a silly precaution, against a pony who could teleport, but Rarity was clearly not at her full mental capacity. Teleporting inside would only destabilize the poor mare further, and possibly put Sweetie Belle in danger.
Clearly, Rarity had snapped at some point during the last twenty-four hours, resulting first in her abuse of Spike, then her perception of Twilight as a twisted monster. If Twilight didn't act quickly, Sweetie Belle might be in danger.
Quickly, Twilight ran to the Town Hall to warn Mayor Mare and get backup, but there didn't seem to be anypony there. In fact, there didn't seem to be anypony anywhere, for that matter. Had there been some holiday scheduled for today, something Twilight had not known about? It wasn't likely, but it wasn't impossible, either. This was one problem with an obvious solution. Twilight changed course, heading for Sugarcube Corner. If there were something going on, Pinkie Pie would know about it.
As Twilight walked in the door, she saw a flash of pink as Pinkie Pie hid behind the counter, her tail still quite visible. Twilight rolled her eyes.
"Pinkie Pie, you're very bad at this whole hiding thing." Twilight paused, before going on. "So, where is everypony today, anyway?"
Pinkie Pie pulled her tail back behind the counter, out of Twilight's sight.
"Please don't hurt me…" her voice was tinged with a certain degree of fear. 'I didn't mean to do anything…"
The normally bubbly pony seemed to be begging for her life. But why? Twilight was unsure. Why would Pinkie Pie fear her? Unless…
Twilight looked at her reflection in the display case. Her fur was a little too dark and her legs a little too long. Her eyes had changed, developing slits, and as she raised a hoof to her face, she saw that it was fitted with a silver horseshoe.
The mirror had been no illusion, after all. Speechless, Twilight backed out of the bakery, then fled. It was true, what Rarity had shown her. Twilight Sparkle was now a Nightmare, whether she liked it or not.
This left the question of what to do about the whole matter. The question wasn't one of who she could trust, but of who would trust her. Surely at least one of her friends would believe her. Maybe Fluttershy…
Twilight heard a squeak from ahead of her, then a pink and yellow blur vanished down the road.
Okay, not Fluttershy.
Who among her friends was utterly without fear? The answer came quickly. Rainbow Dash. Twilight looked around for clouds, and sure enough, the blue pegasus was napping on one nearby.
"Rainbow Dash!" Twilight called out. "I need your help!"
The pegasus woke up, then looked around. "What's the matter, Twilight?" Then she saw her. "Foul demon! Nopony messes with my friends!" The unicorn managed to dodge the attack just in time.
"Wait, Dash, no! You don't understand!"
The pegasus laughed. "Do you take me for such a fool, demon? Do you think you can trick me just by copying Twilight's voice? Now tell, me, what have you done with her?"
Rainbow Dash dove again, and Twilight rolled out of the way just in time. "Dash, stop! I am Twilight!"
The pegasus was undeterred. "Enough with your lies!" she yelled as she dove a third time.
Twilight Sparkle ran for her life, with one of her best friends close behind her, apparently intent on taking it.