…Finally, Pinkie opened her eyes and reached for the valve’s handle. Twilight briefly allowed herself to hope that the party pony had regained her sanity and was trying to shut off the flow of helium. But Pinkie’s hoof fumbled and spun the handle all the way open. “Mmmmrrrrrrmmmmm!” Pinkie shouted into the nozzle, her eyes widening as she inflated even faster than before. She grabbed the handle again, only for her leg to slip off, then stiffen straight out. With even louder squeaks, all her legs inflated, filling with helium to twice their normal width. More and more gas rushed into Pinkie, pumping her as large as an economy-sized bounce house, and then even larger…

Based off of a scene from R-Panic’s story Evil Expandtress, because god-damn did it hit all the right notes for me when I first read it.