Warning, this story contains taboo fetish content that you may not subscribe to. If softcore scat is not something you enjoy reading, turn back now.

While out delivering packages to the good ponies of Ponyville, Derpy is given one of Pinkie Pie's latest experimental muffins to try. Unfortunately for her, it starts to have some unexpected and eventually messy side effects...

Cover art is too hot for fimfiction so It cannot be linked here. If you need it for 'research' purposes, as it involves the same fetish content depicted in this story, look for the artist: 'Kloudmutt' on Derpibooru. It is one of his older works and one of my personal favorites.