Rarity told you to stop by Carousel Boutique to check out some wild new fashion trend that had come down from Canterlot. Whatever you were expecting as you walked into her boutique, it almost certainly wasn't this

You find the white-furred mare as round as a balloon, her four legs sunken into her spherical body up to their hooves and an air hose in her mouth pumping her even fuller. When she sees you she smiles and levitates the hose out of her mouth, shutting the valve to the tank it's attached to with her magic

"Well darling? What do you think, isn't it fabulous~?"