My Little Pony crossed with Breaking Bad:
Several years in the future, a middle-aged Twilight Sparkle is diagnosed with a terminal disease. Facing hospital bills and having severed all ties with Princess Celestia several years ago, and making a meager living as a magic kindergarten teacher, she realizes that she needs to make more money to be able to support Spike.
She sees her opportunity and teams up with Pinkie Pie to produce and sell the popular new illicit drug "Crystal Spark", but runs into difficulties keeping her activities secret, especially since Applejack and Rainbow Dash are leading the Ponyville unit of Princess Celestia's elite anti-drug task force.