Based off the game One Night Stand.

I wake up with a severe hangover and in a room not my own. Next to me is a truly beautiful mare... only I can't remember anything what happened last night.

One day when it is raining heavily outside, Twilight decides to raid Spike's comic book collection and play a while as the Power Pony, the Masked Matterhorn.

She finds herself in the story of how one of the most dangerous villains in their Rogues Gallery came to be. Spurred on by Matterhorn and molded by the Mane-iac, this new villain is unlike anypony Twilight knows how they came to be opposing her.

Art done by EuropaMaxima on deviantart.

That's how long it's been since Flash Sentry went MIA during a mission up north. Twilight has been waiting for him to come back, believing he is still alive. However, others are in need of the Princess more than they need a good guard. Twilight is uncertain how she feels around Flash and waits for him to get an answer to her feelings, but when he's been missing for seven months... one might think something has happened.

King Sombra has returned from his broken state he was left in, and he has taken control of several ponies in order to rise up against the Princess. Driving the whole world to the brink of open conflict, he is bent on revenge for the events at up north at the Empire.

The Mane 6 strive to stop him in order to ensure the success of a peace conference, the last resort to avoid war at their expense. It's particularly bothersome when Sombra has stolen the one thing needed for the conference to be a success.