Solution A:
Have a balanced team, level them up properly and choose your moves wisely.
Solution B:
Cheat!
No. You need to beat the Pokemon League IN the Platinum one.
beat elite 4
yes
you beat the elite four
No.
Yes you do.
in the desert after you beat elite 4
Giratina, and the 3 lake pokemon.
Answer this question to do it!When_the_moon_flashes_red_in_the_slots_game_should_you_stop_lining_up_replays_for_the_rest_of_the_round_or_just_that_spin
you have to beat the elite four plus the champion
By having Awesome Pokemon
you can do about anything after you just cant beat the gym leaders again.