The first story in The Journey of Graves.

Ponyville is getting ready for the arrival of Princess Celestia's marshals, elite of royal guard and travelling heroes of the people. But in all the hustle and bustle of party preparations, a lone traveler slips into town, a young man with business concerning Twilight Sparkle. What that business is remains to be seen, but you can be sure Ponyville won't make it easy for him.
After all, where would be the fun in that?

The storm is breaking on the Horizon.

It's been two months since the battle against Nightmare Moon. Luna is recovering, Celestia is busy turning the government back into a diarchy, and the Mane Six have returned to their lives. All seems well, but when Celestia discovers that half of the power of the Elements of Harmony have been transferred to each of the Bearers, she decides to send thirteen mysterious members of the Royal Guard to monitor them as they manifest and develop their new abilities.

The sins of a forgotten war still linger, and an ancient evil lurks in the shadows, just waiting for the right time to strike. The Mane Six suddenly find themselves once again at the heart of a conspiracy to bring about Eternal Night, and only by awakening their powers and realizing their full potential can they do anything to stop it. Friends both old and new will help them along the way, and an unseen force will guide them as it seeks to right a wrong made thousands of years ago. The Bearer's journeys will take them outside the borders of Equestria and into the world beyond, and when they return, they'll have the power and experience necessary to save the world and bring about balance in all things.

The Powers of Harmony TV Tropes Page (SPOILERS)
The Powers of Harmony Art

Thanks to Wildy71090 for the cover pic.

A horrible Cataclysm has turned all of Equestria into a Wasteland of barren ash and twilight desolation. The Sun and the Moon have been destroyed. Everypony has died--including Princesses Luna and Celestia. But one pony miraculously survives; she is a lone wanderer, the last of her kind, surrounded by menacing creatures that hate her. She navigates the Wastes in an airship and scavenges off the blighted landscape to keep herself alive.

Then one day she meets an old companion who grants her a gift, the chance to go back in time to the warm and sunny days of Ponyville, where her dead friends live in happiness. How far will the last pony venture into this joyous age of Equestria, even if she fully knows that there is no way to change the horrible fate of everypony she loves?

2013 Edition: Smaller Chapters, Better Grammar, and a Few New Scenes

(A shout-out to Vimbert, pre-reader and gentlecolt)

"My name is Lyra Heartstrings, and you will not remember me. You won't even remember this conversation. Just like with everypony else I've ever met, everything I do or say will be forgotten. Every letter I've written will appear blank; every piece of evidence I've left behind will end up missing. I'm stuck here in Ponyville because of the same curse that has made me so forgettable. Still, that doesn't stop me from doing the one thing that I love: making music. If my melodies find their way into your heart, then there is still hope for me. If I can't prove that I exist, I can at least prove that my love for each and every one of you exists. Please, listen to my story, my symphony, for it is me."

Cover pic by Spotlight: askspotlight.tumblr.com