Nightmareverse, Twilight Sparkle, Archmage under Nightmare Moon.

Nightmareverse is an alternate MLP setting where Nightmare Moon has ruled for over a thousand years. A vast, multi-species Lunar Empire thrives under eternal night, blending early industrial technology with magic. Society is stable but controlled, loyalty is expected, and power flows from a divine Empress who has seen everything before. Not grimdark but darker.