All I ever needed to beat anything or anyone was my naturally leveled level 100 Mewtwo. For some reason, leveling them up through grinding made them slightly more powerful than pokemon leveled entirely through Rare Candy. And since most kids I played with used the dupe glitch to level their Pokemon with the candy, I always beat them even if they also used a level 100 Mewtwo.
All I ever needed to beat anything or anyone was my naturally leveled level 100 Mewtwo. For some reason, leveling them up through grinding made them slightly more powerful than pokemon leveled entirely through Rare Candy. And since most kids I played with used the dupe glitch to level their Pokemon with the candy, I always beat them even if they also used a level 100 Mewtwo.
It’s probably due to stat exp. You gain stat points by fighting different mons up to a certain point.
https://gamefaqs.gamespot.com/boards/198314-pokemon-yellow-version-special-pikachu-edition/44331699#:~:text=Stat Exp is a number,individual amount of Stat Exp.