When I played Leafgreen on the emulator, I couldn't win against the elite four and the champion, so I cheated to get masterballs and legendary pokemons. But I remember it didn't help much, but I entered the hall of fame anyway. I know, I was a silly newbie. Of course I don't do it anymore.
And using not very effective moves for dealing damage, especially bug moves to ghost. Bug is super effective to psychic and dark, so I was confused sometimes.