Ever beat the game with one pokemon?

I beat the game a couple times with a team, and now I'm bored. So I decided to play through and try using only one pokemon to beat the entire game. I chose Tepig as my starter, since he's the easiest. I just crossed the bridge to Driftveil City after beating the third gym leader, and I have a level 37 Emboar, who's easily beating every trainer I've come across. If I can beat the entire game with just him, I think I might start again, with Snivy. (The hardest starter.)

) Nice. I know I'm going to have to catch a Legendary before the E4, but I have no intention of using it. Not until after the game is over, anyway. I heard that the order of difficulty for starters, from most difficult, to least, was Snivy, Oshawatt, and Tepig. I'm wondering if I should have went with Oshawatt, since Emboar is just about one shotting everything. I was hoping it would be *a little* tougher.