*Celestia found herself in a room filled with naught but darkness, unable to see her own hooves in front of her. It felt hot, uncomfortably so, nearly burning her body as she tried to discern something from the shade. She felt an overwhelming sense of dread, a horrible, repressing, contrasting coldness in her heart, ascending right through her non-functioning horn. She could feel something around her, but she couldn't see anything, or hear anything. Just... Nothing.
The coldness tightened her heart, and her breath came shallow and slow as the burning intensified. At last, a sound came to her, but it was no comfort.
'The world has changed so little in such a long time,' resonated a chilling and deep voice, rattling her to the core. 'Sinners, villains, demons... No different than before.'
Celestia tried to call out, say anything, even scream if she could, but her voice was swallowed by the infinity. This was a fear unprecedented for her- not for her ponies, not for her sister, not even for the future, but for her very life. She drew her hooves close, feeling insignificant, terrible... wrong. The darkness vanished, replaced by a violently bright light, more intense than any she'd ever given the sun.
'And such pitiful beings to claim for themselves dominion,' A different voice intoned, overlaid with thousands of others in an eerie chorus. 'To think that this would happen in our absence. It is a shame.'
The alicorn felt her heart plummet, as if she fell into an abyss below, the burning and the cold drawing tears from her eyes. Who was doing this? What was doing this?
The chorus spoke. 'It is time we returned to the world, their 'Equestria.' My Earth fits them not. Perhaps the child's sacrifice will amount to something after all this time.'
The resonance laughed, and replied, 'And my beasts will make sure of that.'
The voices spoke in unison as she felt her body succumb to combustion, and her heart start to freeze, but now they spoke to her. 'This is your judgement day, Equestria. We will reclaim your world, and return it to the dust from which it came.'
And then Celestia awoke, sweating through cold fur. And the vision faded, leaving only the dread in her heart, and the sense of imminent doom she could not shake.