"Hey... can I ask you something Dom?" Jen asked, standing on uneasy legs. She's still recovering from her orgasm, but the only thing she can think about is having another. And then another, and another, and...
"Sure, anything." Dom said, reentering the room. Jen's cock stiffens when she sees that he's only wearing his boxers. There's a slight bulge from his own equipment. The sight only renews Jen's corrupt thoughts.
"Transform or Dare?"
"Huh? You mean that stupid legend? Jen, that's..."
"Sorry not an answer, now you get both! For your transformation, you'll turn into a dog from the waist down. And for your dare, I dare you to forget I was the one who transformed you." Jen smiled as the changes took hold. Dom stared, not really seeing or comprehending the world around him.
His boxers were becoming to tight on his growing body. White and brown fur grew on his legs, which popped backwards to a digitigrade stance. Dom's feet stretch, thick, black pads forming on the ends of his toes. Short claws burst from his new paws, as more fur raced up his body. The fur slowly ran into his "happy trail". Jen, her own horsecock erect and her tail wagging, walks up to Dom and helps him by removing his now skin tight boxers.
He sighs in relief as his balls and cock are allowed to flop forward, both engorged. His penis is then snapped up to his abdomen, where a furry sheath grows up concealing it. His nuts, previously about the size of typical chicken eggs, have doubled in size. They swing between Dom's thighs, full and heavy. Every once in a while smacking against his inner thigh, causing Dom to yelp in pleasure. Though he doesn't have a canine tongue, he lets it hang out the side of his mouth.
Jen can't wait any longer. She slides Dom's new canine rocket into her horse pussy, and wickers as it starts to become erect. Her own cock smacks against both their chests, spilling cum down their bodies.
"Jen, what the..." Dom snaps out of his trance and stares at his girlfriend, who is riding his transformed penis and has her penis tickling his nipples. Dom knows something is off, he can feel it. The way his member feels inside Jen's pussy, something isn't quite right about it. But holy shit does it feel good.
Dom's knot swells, locking the two in for the duration of the fucking. Not able to pull out completely, Dom starts humping Jen, his thrusts more powerful than before. He lies her down against the bed, pulling her tail and licking her shaft.
Jen whinnies in approval, her hands busy teasing her nipples. Dom takes her cock in his mouth and sucks. All it takes is one good suck for Jen to cum. Her cunt clamps down onto Dom's canine dick, which then swells even more as his own load is sent flying from the tip. Jen's eyes roll into her head as she feels her enormous pussy eating up as much of Dom's spunk as possible. The two remain wrapped in each others arms while they wait for his knot to deflate.