There was a strange humidity in the air. Something that didn't depend on either of the ponies there, something that seemed to be there completely by chance. A simple yet uncommon weather phenomenon. It made Twilight's mane fuzz up a little, though the stress of the situation probably didn't help. If they had been cooking something, they would have noticed it there too. The kind of weird humidity that made water not boil quite right. The kind that was a minor nuisance to deal with on a normal day, in a normal life. In a common life. Theirs were and had been anything but, especially so for one of them.
Twilight looked towards the distance, towards the end of the structure opposite the one she'd entered from, where the river once had left the lake once there. She couldn't see anyone yet, but she could sense something, maybe someone. Stella had made it so. Something vague, but a presence nonetheless. A powerful presence, in odd ways, ways she couldn't quite place or identify as she was not allowed to, though she was not allowed to realise her perception was being altered as such. And something else. Some odd familiarity, a sense of recognition. Part of it for obvious reasons not obvious to her, part of it memories not quite suppressed, yet not quite perceived.
Then she began to see something, too. Vaguely at first, an indistinct shape and blurred colours, or at least what her brain interpreted as that. It was deliberately altered, distorted, incomplete information. A vision slowly revealing itself. It was confusing. It was frightening. It was fascinating. It was different from anything Twilight had expected to see, and despite herself she could not help but feel some level of awe at the sight, despite how little she could manage to rationally place the events leading to that moment in line with what she was experiencing right then.
Stella's steps only began to make sound when she was a few metres from Twilight. She stood tall, about as tall as Celestia, her mane and tail a flowing purplish nebula of light and stardust. Her hooves were clad in black, glassy metal, a material that reflected the light in such a way it looked pure white from certain angles, its exact shape never quite coming into focus. Like living matter roughly caged into a shape, like the fabric of the cosmos condensed. The same material adorned her neck and made up the crown above her head, its jewels miniature stars in shifting colours. Her coat was a flaming pink purple, vibrant like an ocean, and her eyes glowing pools of light.
Some part of Twilight's mind told her she should have bowed at the presence. The rational part of it refused that. So she stood and stared down the alicorn as she was approached, and finally as the other stopped she chose to be the first to speak, pushing past the intimidating aura she felt herself pressured under. "So you are the one behind those attacks, and behind the theft at my laboratory. Who are you, and what do you want?"
"I am Stellaria." The alicorn spoke and her voice reverberated through time, echoing backwards and forwards and drowning Twilight from all around her. "Rightful ruler and leader of this world, soon to be Empress of Equestria and all surrounding territories." There was disdain in her expression, if subtle, in the way she looked at Twilight and spoke to her. "You would be correct, Twilight Sparkle, it is indeed my work you have observed. I have come to liberate this world from you, and take my place where you unjustly stand."
Twilight wanted to speak again, but she was interrupted by two things appearing before her in the air. One was a black, metallic cube, hints of lines along its surface. The other was a folded piece of parchment. Stella levitated both towards her. "You have seven days to open this box and reveal its contents. I care not for the method you choose. For every day you go without succeeding, save for today, I will at sunset destroy one of the cities marked on this map." She seemed to smile. "I believe this will be a worthwhile exercise in proving your unfitness to rule." Her form began to disappear as Twilight took hold of the objects she had been passed. By the time her next sentence finished, she was fully gone, leaving Twilight confused and angry and alone. "I shall choose an appearance more befit to grace unworthy eyes of mortals like those you surround yourself with, and to witness your progress or failure I will return later."