If you already beat the game, just battling the Elite Four is a great way if you can take the repetition!
Train your pokemon.
level 100
level it up to level 21
any level up to 100
level it up
level up or action replay
level your Pokemon up to 80
You have to get Piplup for the starter Pokemon and level him up or trade for it.
Level it up to level 34.
you battle and level it up
To evolve turtwig [pokemon pearl/diamond] level it up to level 16.
umm.......i think.....you.....TRAIN THEM UP!!!!!!!!