Now, I hope you know what an only run is, but if you don't, then I'll enlighten you. An only run is when you beat your game with only one Pokemon. You can also have some HM slaves, but they are not allowed to fight, with the exception of double battles. Now, here is where you brag about having beaten the game with one Pokemon, talk about your progress in this, or just request a good Pokemon to beat the game with.
For example; I am going to beat Pokemon Diamond with a Budew. I did it before, but I restarted the save file, and I cheated a bit, soo yeah. Also, by the way, this section is only for fourth generation only runs. So, have fun!
By the way.. it's really easy to beat the game with a fully evolved starter.. but try something difficult! Maybe a Bibarel, or a Starly? Perhaps even a Kricketot!