...have a tendency to go awry in the most unexpected of ways.

When the Crystal Heart's power destroyed King Sombra, all of the Empire rejoiced. Little did they know, they had played right into the ancient tyrant's hooves.

Having over a millennium to plan, Sombra knew that if a pony managed to get past his traps before he could reconquer the Empire, their was little chance of him surviving. So, he let himself be 'killed', in order to get closer to his true goal undetected; the Umbrum trapped beneath the Empire.

Hiding as just his horn, Sombra laid low in the very heart of the Crystal Palace, biding his time, until the entrance to the underground section was opened by the new Crystal Princess and another princess with a purple coat and familiar magic. Recognizing that magic as that of the pony that foiled his most recent efforts, and knowing of only one princess-to-be with a coat that color, Sombra swears to make Radiant Hope pay for moving against him once again.

Using his magic to reach the deepest depths beneath the Empire, Sombra reached the sealed Umbrum undetected, and reformed his body. Having devised a way to free them during his own imprisonment, Sombra began so, fulfilling his goal even without controlling the Empire. Bursting free in a wave of shadow that left no doubt of their return, Sombra gives Cadence a message for Celestia before following his own subjects into the night:

“Give this message to the Two Sisters. Deliver unto me the princess that yet again hindered my efforts to free my people to me within a week, that I might exact my revenge against that traitorous Radiant Hope, or I shall show all of Equestria why the Umbrum were so feared!”

However, when a week passed, and Sombra found out that the princess in question was not Hope, but rather a new princess named Twilight Sparkle, he finds his plans for revenge derailed. Bound by his word, when she offers to go with him to prevent a war, he finds himself with a 'prisoner' against whom he holds little ire.

And as time passes, Sombra begins to see that he and his 'guest' have more in common than he initially thought.

AU as of Chapter 34 of the 'Friendship is Magic' comics.

A queen will do a lot for her subjects, even give up her own child if it meant giving them a better life, despite the obvious pain that causes for the children in question.
That is a pain Twilight Sparkle never felt, as she grew up never knowing that her loving family had adopted her. And while those connections remain, as secrets become revealed, Twilight cannot help but wonder about what never was, as she attempts to reconnect with a family she never knew she had. Even if that means admitting that she, herself, is a monster.

Inspired by the story 'Change' by tom117z

Searching for any records King Sombra may have left behind, Twilight learned of the shadowy king's tragic past. However, she also discovered his horn, in which his mind and remaining power were contained. Determined to learn how to use his Dark Magic for Good, Twilight brought Sombra back to Ponyville with her. After all, what could he possibly do as a horn? ...Or will he stay that way?

Edited by Darth Vendar and Myrkur
Inspired by Issue #1 of FIENDship is Magic
Gore tag just to be safe.

Edit 06/15/23: Now in the top 2K stories on the site, by rating! Thank you all!

A mirror between worlds shattered. A girl driven mad by power ripping holes between worlds. A spiteful mare traveling through time to get revenge. When the fabric of reality surrounding Equestria starts to come unraveled, it falls to Twilight to find a way to fix things.

Good thing she has a familiar face to help her. Several of that face, actually. An alicorn princess (canon Equestria), a human mechanical genius (Equestria Girls), a brilliant but irritable slacker of a unicorn (Reflections), a stallion no less intelligent or magically gifted than the rest (genderbent Equestria), and even a unicorn obsessed with Dark Magic, working together to save all of their worlds, by returning Harmony to the world they find themselves in.

A world where Nightmare Moon rules Equestria after sealing Celestia in the Moon, only to go to war with the Crystal Empire, against King Sombra and his Umbrum army. A world where Discord wrought havoc, until his powers were stolen by Lord Tirek, who rampages across both sides of the war indiscriminately. A world where even the ponies far from the fighting must constantly fear Changeling attacks. A world where Harmony is nothing but an empty dream.

A world where Twilight Sparkle never existed.

What could possibly go wrong?

Contains spoilers for the cartoon, comics, and movies.