Ty's feet arc up and become digitigrade. His arms cover in fur and his hands turn into paws. His nose changes.
All the while, still having sex with the tigress.
But that wasn't all. He was feeling a greater and greater connection to the tigress below him. Starting in his penis, through his tiger belly and spine, up into the back of his head and filing his mind with her scent. The connection grew stronger and stronger with each thrust.
His eyes changed and long whiskers pushed out of his face. He opened his mouth and roared.
He could feel her, completely, physically. They were one. The same. His face pushed out and fur covered the last of his human skin.
He came.
Ty clumsily rolled off the back of the tigress, his wish's conditions and results now complete. He was a tiger, a very male tiger, and he just had sex.