the Weird Gym rule (Possible pokemon transformation)

he then remembered hearing about a Gym Leader rule that is often forgotten because it is so rarely used, said Saying that if you win they would give you their strongest pokemon but if you lose you would become their pokemon forever, and what pokemon that was or what gender would decide the Gym Leader themselves.

A shiver ran down Ash's spine as he thought about the rule. He had always been confident in his abilities as a trainer, but the prospect of becoming a Pokémon forever was daunting. He tossed and turned in bed, his mind racing with the possibilities. What kind of Pokémon would he be turned into? Would it be a powerful one, or a weak one? And what Gym Leader would he have to face? He threw off the covers and got out of bed, pacing back and forth in his room as he tried to shake off the feeling of unease. He stopped in front of the window and looked out into the night, the streetlights casting long shadows on the ground.

and then Made his decision he would start tomorrow with his charizard at his old friend Brock's Gym.

He let out a deep breath, his decision made. A sense of determination washed over him, and he felt a thrill of excitement mixed with a hint of fear. He turned away from the window and walked over to his bed, where he sat down and pulled out his Pokédex from the bedside table. He flipped through the pages, stopping at Brock's entry as the Pewter City Gym Leader. He read through the information, his eyes scanning the paragraphs, re-familiarizing himself with Brock's battling style and his typical Pokémon lineup. As he read, his mind began to wander, thinking about the possibilities of the battle to come.

(the next day)

Ash stood in front of the Pewter City Gym with charizard's Pokeball in hand since under the rule every battle would be 1vs1.

He gazed up at the imposing structure, the Pewter City Gym's stone façade gleaming in the morning sunlight. The entrance, a pair of large, metallic doors, seemed to stare back at him like unblinking eyes. Ash felt a shiver run down his spine as he realized the gravity of his decision. He took a deep breath, the cool air filling his lungs, and steeled himself for what was to come. With Charizard's Poké Ball still clutched in his hand, he reached out with his other hand and grasped the door's icy metal handle. The door creaked as he pulled it open, the sound echoing through the stillness.