you need to beat the elite 4 and the champion and see every Pokemon in sinnoh(you should be able to if you fight every trainer). for palkia, go to celestic town and speak to the village elder. then go to rowans lab. you should get the national dex there. then go to the snowpoint temple. the guard will stop you but candise will say some things and you can go in. to get to regigigas, go DOWN, not UP.
You can get it at the snowpoint city temple at the bottom of the temple.
in the ice temple in snowpoint sity
You Can't... that's in Pokemon diamond/pearl/platinum
beat the elite 4 dips hit
First beat the game then get the national dex and then you can go in!
You need to have all 3 regis and go to the snowpoint temple.
Regigigas in snowpoint temple
You have to get regice, registeel, and regirock. Then go to snowpoint temple in Snowpoint City and go to the bottom, bring the Pokemons.
You can find Regigigas in Snowpoint Temple in Pokemon Diamond, you will need to bring Regice, Registeel and Regirock for Regigigas to waken.
First get the national dex then beat th elite4
You'll be able to go inside Snowpoint Temple. Regigigas will be in there.
You can catch on at the Snowpoint Temple. However, you must have the 3 Regis in your party.