We are having an explosion of dengue cases in Latin America propagated by that mosquito, it is not a nice disease and immunity doesn’t really work, depending on your luck. Good luck everyone!

It’s on purpose, from the movie “A Serious Man”

https://youtu.be/6HJqPZ-KmZs?si=b23iXKns4HBF5SRO

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.