It is possible to get every pokemon from Platinum by wild encounters, or seeing them in a trainer battle. By the time you defeat the champion, the pokedex should be complete. Usually, however, it wont be because maybe you didnt battle everyone, or something. In that case, do one of the following: 1) go back … Read more

It depends on your team. My team is Luxray, Roserade, Infernape, Gardevoir, Crobat, and Gyrados. I have caught a Giratina, Dialga....etc, but I don't use them, and I have won many battles with my team.

You have to use a shiny stone, most easily found in iron island. By the time you get to iron island, your pokemon should be around level 38 or more.