After a tragic accident claims the lives of Fluttershy and Big Macintosh, Twilight Sparkle begins to grow distant from her remaining friends. She locks herself in her castle and spends her life working on a cure for aging in the hopes her remaining friends can be saved.

Meanwhile, Pinkie Pie comes up with an idea for the best surprise ever. For three years she works in secret on a surprise for Twilight Sparkle. But Twilight's gift won't be revealed until the last of her friends has passed away.

What kind of surprise could possibly make up for the loss of your best friends?

Long before the knowledge of Celestia, an evil came to be. In the darkness, its power grew and so did its hunger. Thousands of years later, it awakens and threatens to devour and destroy all life.

When Celestia, Luna and Discord are defeated by the monster, Twilight Sparkle and her friends confront it, only to find that they are severely outmatched. Just as she begins to lose all hope, Twilight remembers a spell that could be powerful enough to defeat the monster, but only at a terrible price.

Pinkie Pie is dead. After a three week battle with an incurable disease, she finally passed away in her sleep. Now at the funeral, her five best friends are going to tell the story of the party pony's last days.

Rated Teen to be safe.
Thanks to damandust11 for making sure this story is at least somewhat readable.