You continue to thrust, looking at him under you in the mirror. You notice something odd, his cries have turned into moans of pleasure as his ass has seemingly grown to accommodate your cock. But something even more strange is happening, his extremities are starting to turn black and his arms look slightly shorter? You shrug it off as you continue to thrust, nearing orgasm. Suddenly you cum, hard. His stomach bulges as it fills with cum but then he looks in the mirror in fear: he's starting to change as well. His bulging stomach begins to darken, his face and limbs become completely black, and his hair begins to fall out. His stomach begins to seemingly empty as his arms get shorter and shorter, his asshole fusing with your cock. His legs start to darken as he lifts them up, touching them to your balls. His legs start to fuse with your huge balls, eventually completely fusing, your balls were now the size of yoga balls and almost touched the floor. The darkness started to spread up his torso as his arms completely receded into his body, eventually reaching his shoulders. His body started to round out and get a little veiny, seeing this in the mirror caused him to shreek in horror. The darkness spread to his neck, causing it to thicken to the same thickness as his cock body. It felt like there was a lump in his throat as his head darkened to match the rest of him. He watched in the mirror as his face began to flatten and flare out, his head now matched his horse cock body, only his eyes still remained, still weaping. suddenly his former throat closed up with pressure, and you came a huge load out of your new 6ft cock. As you came, his eyes disappeared, he was gone, now your giant cock.