A short story where Nightmare Moon suddenly returns after an untold amount of time has passed.
In a desperate attempt at total control she banishes both Princesses, and then goes on a rampage through Equestria.
Those that don't willingly bow before her are indoctrinated in order to do her bidding without question.
Any signs of rebellion are stamped out and the participants are publicly executed. That would include Anonymous' (yours).

You, along with your ragtag team of rebels make what seems to be a final assault upon Canterlot.
Unfortunately... you're unable to carry out your task... but the event will be engraved in Nightmare's Memory forever...
The brothers and sisters who followed you under the Banner of the Sun are killed or will never gaze upon the moon of eternal night again.
But you are the exception, she had better plans in store for the one who wounded her.
Instead of granting you the sweet release of death she's forced you into serving her.
She threatens you with the town and the ponies that first took you in when you landed in that world, solidifying her influence over you.
But, even though she's won, even though she's managed to make you guard her with your life... you're anything but done.
You will bide your time, you will wait for the perfect moment, and when that time comes you will make sure Nightmare Moon will regret letting you live that day at the gallows...

Warning: Clop with plot focused around Anal Intercourse.
Warning: Could probably be made into an actual story by someone willing to do so.