Fight the elite 4 and just train your Pokemon
You don't. You can only catch Regigigas in Diamond, Pearl, and Platinum.
in the snowpoint temple
that doesnt make sense
you need REGIROCK, REGICE, AND REGISTEEL.
You have to have a special Regigigas from an event.
you need event regigigas
No; you cannot catch the three Regis in Platinum, UNLESS you have obtained a special Regigigas through some special events.
only with a hacking device.
Trade with Pokemon Platinum, Pearl, or Diamond.
I'm sorry but you only have one chance to catch him
You need a event Toys R Us Regigigas.
You can only catch it in Ruby, Sapphire or Emerald and migrate it over. If you get an event Regigigas on Pokemon Platinum you can catch Regice there.