get the other game or the same game and start the game 3 time if u want them on one or start it 6 time and trade them over. You can also get a friend to do this method with you
You can not catch any of them in black or white, but I think that you can catch all 3 in diamond.
You can't catch a starter Pokemon. But to get all of the starters you can trade the Pokemon to another game and restart the game you were playing and get a different starter.
you've gotta be crazy if you think someones gonna write all the Pokemon you can catch in diamond
you have to catch all of the pokemon in diamond or SEE all of the pokemon
Catch them all.
WITH POKEBALLS MAYBE?
Only on Pokemon yellow.
You can do this: get a gam to trade with ( soul silver, heatgold, platnum, diamond, pearl) start your game choose a starter catch another pokemon and trade it to another game, restart and repeat process until 3 pokemon are on the other game, then trade them back to platnum
Action Replay
If you already have a turtwig then all you have to do is catch a wild chimchar. Get a poke ball (or any other kind of poke ball) and fight till its health is low then catch it.
no
get an action replay, get the Pokemon modifier cheat for it, then catch all the Pokemon.