(Old song, new story. Deal with it.)
An infection featured in the Ponyville newspaper indicates that there is a disease spreading (or starting to spread) across Equestria. And the terrible fate that happens to Ponyville after it is reached is darker than expected, and only can be viewed in Tombstone's memory.
But what if his memory just lied to him? What if it was just twisted and wasn't meant to be?

Well, that calls for a sequel, don't you think?