Fifteen is ancient for a dog, and Spike's starting to feel it: sounds and scents getting a little muffled, a little soreness in his hips, a gnawing little pain in his stomach that he hasn't told Twilight about even though it's been getting steadily worse the past few months.

In Equestria, though, according to Twilight, a fifteen-year-old dragon is still considered a child. And as she's been pointing out for the past five or six years, the portal to Equestria is right across town...

My entry in FanOfMostEverything's A Most Delightful Ponidox contest, this story didn't finish in the Top Eight.