A rather less cheerful, more Cronenberg variant:

Mature Content

It was to be the first trial of human teleportation using the same data transfer methods that moved pokémon between the pokécenters via the computer system. Bill knew something had gone horribly wrong the moment he began to rematerialise within the receiving booth. His beloved pokémon, Buttercup, was no longer in his arms. He'd chosen her to join him in this historical endeavour and now she was gone.

His skin was no longer his own. Organs were not where they should be - only a void between his stunted, animal-like legs. Staggering from the receiving booth, he caught sight of his reflection and screamed. Arcs of lightning burst from the yellow fur coating his body, frying the delicate machinery of the teleporter.

He had to get help. Nurse Joy would know how to fix this. She had to...

He had staggered halfway down the trail towards Cerulean city when he met Officer Jenny racing the other way, evidently drawn by the explosion on the hilltop laboratory. Her police whistle was to her lips as if ready to blow it, though at fell free at the sight of him, as her mouth fell open in horror.

"Please help," Bill tried to gasp. But all that came from his rodent lips was "pika chu." His eyes widened as she selected an empty pokéball from her belt. "Pika pika! Pikaaaa!"

The ball caught him in the chest, turning him into digital energy for the second time that night, sucking him in, and snapping shut. Unlike the teleporter however, the pokeball was calibrated only to acquire pokémon DNA. Faced with the fused entity, it left his human DNA behind in the dirt, storing only a perfect, healthy specimen of a female pikachu, Bill's genius intellect forever trapped within its ratlike body.