@Polla
 
There’s one with a happy ending and another one where the ending is about as depressing and grimdark as possible. Celestia murders the Wonderbolts during a public display, beats the Mane 6 to a pulp, then flees to the wilderness. She dies of starvation.

@Pollodiablo:
 
>Tyrant.
 
Son, you best be referring to Discord.

Awesome Celestia

@Takashi.0  
There was one fanfic where Celestia got mind-raped by Discord in a similar way. It was called… Scented Venom? Or Heavenly Turmoil. It was one of those two, anyway. Although if i remember correctly it has a happy ending, not a sad one, where the evil tyrant gets to sit on the throne again. :>

chaw haw haw
 
But no seriously your post is amazing. Fund it

DAMMIT IMPIOUS!

VV In my headcanon, Celestia stays a kind ruler thanks to a metaphorical ASTEROIRD-SIZED AMOUNT of self-control.
 
It’d make the main theme for an awesome fanfic idea with Discord using his mind-rapey skills to take that self-control away, allowing her to vent out at least a thousand year’s worth of hopeless despair for her sister, immortality-related loneliness, frustration that comes with the stress of being a monarch, and just general RAGE, leaving Luna and the Mane six have to fight her “Nightmarified” self and eventually forcing Twilight to snap her out of it using the power of (pseudo-mother-daughter) love.
 
Bonus points if she serves a contrast to Nightmare Moon’s suave, calm persona by being little more than a mindless berserker who wants to burn the world to a crisp with endless day.
 
Bonus Bonus points if you can see her struggling to regain her sanity, via Berserker Tears.

I’d like to think Celestia is more in control of herself than Luna, but if she were to give in it would be terrifying.
 
They owe her everything. She owes them nothing.

v In place of a Dark Lord you would have a Queen…

It happened to Luna because she felt unloved and unappreciated. And if that’s what can happen to an alicorn who simply doesn’t feel loved, imagine what could happen with Princess Celestia, who gets branded an evil tyrant no matter what she does?

Maybe. *gulp*

Could Nightmarification happen to anyone? Considering how nice ponies are, it must be incredibly rare, but I imagine such a thing could happen to very powerful ponies glances nervously at Twilight and Dash