After pulling out of Gracie's holes you were penetrating into, you take a second to catch your breathe after all the shapeshifting you did while trying to make your boyfriend's sister cum 30 seconds after you humped her that many times. You thought you would be done, but your body suggested otherwise as you felt something.
All of a sudden without warning, you lose control of your own shapeshifting, while you were getting taller than Gracie, because you were at the same height as her while you were penetrating both of her holes at the same time. Just then, you also sprout muscles while both of your penis's become 1 large penis which was longer than both. Gracie started drooling, as she suddenly became hypnotized by the massive elephant trunk sized penis you now had, which made her sit on it without resistance.