in platinum yes pearl/dimond no unles have AR
Save in front of Giritina and battle it. if it isn't a shiny, turn off the ds and try again. It will take a long time.
he will be saved on your pokedex as seen but you will never get to capture or battle him in the wild again and that is for all legendary Pokemon
Once you have defeated him in battle there is no other way to fight him again unless you saved before the fight with heatran.
go to the next level or play again
Sher Shah Suri defeated Humayun in the Battle of Chausa in 1539. In 1540, he again defeated Humayun in the Battle of Kannauj and became the Emperor of India.
There is one way how to battle Giritina again and it's on turn back cave located close to Valor Lakefront, but the only way to get there is defeat the league.
If you have already caught them and saved, you cannot re-battle them again. If you made them faint, you have to battle the Elite Four again to make them respawn.
Other than cheats, you can't
Pompey was defeated by Julius Caesar in Italy and again at Pharsalus in 48 BC. He escaped to Egypt but was killed there by order of Roman Dominated Egyptian Government.
beat it again. nothing will happen
wait for a long time then try again (it helps to save before you "talk" to uxie, this way if you defeat it all you have to do is turn off your DS system and try again)
Once Red is defeated, go to the league and beat them then he will apear again.