I'm not sure why you'd want to do this, but I think I found a way to be able to easily beat any Pokémon game, and all you need is a friend who's willing to help you.
So basically your friend trades you a good Pokémon, like Riolu, as an Egg. You hatch it (so you're the OT) and then trade it back to him. He evolves it, EV trains it (optional), and levels it up to 100. Then he trades it back to you, and viola, you can OHKO anything.
Would this strategy work? Or does it have flaws (besides taking the fun out of the game)? This would probably be useful to some people, if for some reason they were forced to restart their game.