I started a playthrough of Emerald instead of Sapphire, but a few days ago, I also started a "no evolution" challenge of Leaf Green. I use the term "no evolution" a bit loosely because in Gen I Kanto, Pikachu and Clefairy weren't evolved Pokemon, but they are in Gen II onwards. I spoke to a friend of mine about it, and he argued baby mon don't count as long as I'm not using a mon with more than 350 base stat total. Hitmonlee doesn't count, but Pikachu and Clefairy do. Porygon's one of the few from the game (outside of post game stuff) that does evolve but has too high a base stat total for the challenge.
It's obviously going to get harder later on, but tonight, I beat Gym Leader Erika before she could declare a single attack. Abra's Psychic beat her Victreebel and her Vileplume, and Vulpix's flamethrower beat the Tangela in-between. It was awesome!