you can get celib in Pokemon with out action replay once you get the code hold l and walk in the gress (Dont run) in the grass while your holding the l it will freeze the game
u will need action replay and hold L+R while walkling into pokemart and this guy in green will give this item called oak's letter then you go to rt 224 and he'll wait there and shaymin will appear...
You can find Giratina in the Distron world, you have to battle and win against Cyrus, the Team Galactic's Boss and then you will be able to battle and catch Giratina.