Mary took both the kangaroo vial and the gender vial - had to be a female, or the kangaroo wouldn't have a pouch - and mixed them in equal parts into the glass. She took the drink to Brett and said:"You look tired...here, drink this and you'll be ready to jump." Not paying much attention to the drink he was being offered, Brett drank it down casually while keeping his eyes fixed on Mary. "Now, just relax and let the drink sink in a bit...", Mary said while rubbing a calming paw across Brett's shoulder. Suddenly, Brett could see his skin turning darker and darker into a deep brown color. He touched the skin on his arm, and it felt exactly like the tigergirl's skin. Brett started to panic, but Mary reassured him that it was alright and positioned herself on his lap to prevent him from running away in the meantime. Their gazes met right as Brett's face began to expand into a black-nosed muzzle, sleekly built with two short pointy ears. A ripping sound emerged from Brett's shoes as his feet grew many times their length and became huge, flat hopping feet with claws at the ends of his large toes. Brett's form really began to barrel now, and it didn't look like his clothes would hold much longer so Mary tore them open, releasing the huge ball of rubber that was Brett's new torso. His arms had already finished changing, ending in tiny paws that could barely grasp anything. "Okay, stand up for a moment", Mary said to the seated Brett, "'cause it might get painful if this continues in your current position." Doing as instructed, Brett stood up, landing with a thump on his enlarged feet. A small point now started appearing in Brett's pants, pushing further and further outwards until the seams of his pants started ripping. Then, with a loud rip, a huge kangaroo tail definitely pushed through a hole in his pants, quickly extending in length and slumping on the floor behind him. The kangaroo potion was now done - now the gender potion kicked in...
His marsupial member he had been staring at for a while was disappearing as fast as it had come, quickly shooting upwards into his crotch and ballooning into female internal organs. All that was left on the outside was a slit, rimmed by two large rubber edges. But to Mary, the most important change occurred when a piece of skin separated itself from Brett's (or should we say Brenna's) stomach and turned into a huge kangaroo pouch. While Brenna was still looking around in confusion, Mary did not wait to try out the new kangaroo's main feature and leapt straight into the pouch. "Hmm, actually kinda comfy in here...more than I expected anyway", Mary said. Brenna sighed (as far as she could do that in her current state) but knew there was no way to return to normal except by accepting her new mistress.