"Wait, before we do, I want to try something. Wait here." Mary said. Kevin was confused, but allowed her to run off into the other room. Watching Mary's fat, hairy body run made him harder. Her massive pig balls bounced all over the place, and her pussy leaking its juice all over the carpet. Kevin continued to stroke his own meat until Mary returned with two glasses in hand. One was a darker shade of green than the other.
"Up for a little adventure?" Mary held out the darker glass for Kevin. He hesitated to take it. He guessed Mary was offering more of the vials to him. He just wasn't sure what it was. It smelled very... familiar somehow.
"Come on, please Kevin. I promise, it'll be fun for both of us." Mary pleaded. Kevin couldn't refuse her, as Mary pressed her breasts up against his chest. Milk began to run down his body, the warm liquid trailing down past his stomach, to his cock and then his balls. Kevin downed the glass of green liquid in one gulp. Mary followed suit.
"Oh fuck Mary, I'm so," oink, "horny. I need to fuck again!" Kevin exclaimed, feeling his boar cock stiffen immediately after finishing his drink. His beastly mind has taken control, he can't stop himself now. His cock slides underneath Mary's, until Kevin's shaft is rubbing the underside of hers. Mary squeezes her legs together, pressing Kevin's cock closer to her own. The heads of their cocks touch, and the two are almost overcome. Mary reaches around to pull Kevin's head closer. He snorts into one of her floppy pig ears, and then playfully nibbles her ear.
"Oh... that... it feels so good... Don't stop!" Mary started gyrating her hips so that her cock and balls massaged Kevin's. As she did, Kevin gripped his sow's sides and lifted her up. His porcine nose got a better whiff of her wet pussy, and he knew it was time. His cock started to gradually move backwards, closer to her dripping lips.
That's when the changes began. Mary felt her body growing again. But rather than gaining fat, her muscles became more defined. Her long, wiry pig hair retreated until she had a fine coat of bay hair. Kevin's body did something similar, only his new coat was entirely black. Both felt their ears stretch upwards, closer to the tops of their heads. Kevin felt his nostrils expand, though his nose retained an overall piggish cast. His hooves melted together, until he was left with one large hoof.
"Horse, she gave us the horse vial!" Kevin realized. And what's more, she'd also given them each a dose of male and female. Mary licked her thick lips as she felt her cock and pussy grow. They were already large. Her cock lost its spiral, but gained a thick mottled sheath, and a flared head. It was three inches thick, and 2.5 feet long. Mary felt her balls plump up, filled with a mixture of horse and pig cum.
Both her piggy pussy and asshole puckered and inflated. Her netherlips turned black like her cock, and reshaped so that they were the typical teardrop shape. Meanwhile her asshole grew until it looked like someone stuck a black donut between Mary's cheeks. Above her ass, Mary's pig tail grew long bay hair, until it looked like a mixture between the two animals.
Kevin saw Mary's changes, and eagerly awaited his own. While he was expecting his cock to change, there was an odd pulling feeling below his asshole. His hand reached around, and he moaned as he touched his growing pussy. It was enormous, the outer lips so thick. Kevin had no trouble sliding his large hoof-hand inside himself.
"Oh... yes! God please fuck me Mary! I'm so horny! Please, I... I need you inside me. You... you can fit! There's room!" Kevin cried as his hand furiously pumped in and out. Mary was more than happy to do as Kevin asked.
Mary walked behind Kevin and lifted him up. Her body's new muscles had no trouble supporting his weight. Kevin's hand exited his new pussy as Mary prepared to nail him.
"That's right, get your leg up Kevin. Christ, just look at your piggy pussy! No... it's a mare vagina!" Mary watched in awe as Kevin's new slit transformed from porcine to equine. The shape changed, the bottom drooping significantly until it was just like Mary's.
She was quick to slide into him. Kevin oinked and moaned as he was being fucked for the first time. It was incredible, Mary was filling him so much. Every time he thought she couldn't go in further, she did. Until all 2.5 feet of her horsey sausage was inside him. Kevin felt a bulge in his stomach where Mary's cock was. And then she started pulling out. Kevin whinnied, his cock cumming and his vagina clamping down on Mary's cock. She held out, and slammed back into him.
Kevin kept cumming as he was overwhelmed by the sensation of being taken. His cock spewed horse-pig spunk everywhere. His mare cunt unclenched over and over around Mary's shaft. She was pumping so fast, she thought she might get a rub burn. Mary at long last came inside Kevin, causing him to blackout completely. Hot seed was swallowed up by his snatch. Mary's own pussy wept, fluid freely pouring from her pussy.
She carefully slide out of Kevin once she was done ejaculating her load into him. She let Kevin crumple to the ground exhausted from their most recent fucking session. Mary smiled, and laid down next to him. The two horse-pig creatures snuggled up beside each other. Both dreaming of more intense love making, and having lots of piglets or foals.