How do you get Regigigas in Pokemon Diamond?

Answer 1

Firstly you need to complete the game, and then transfer the Regis to diamond and put them in your team. Go into the temple in snowpoint and go to the final floor, and Regigigas will be waiting.

As for Regigigas, he can be summoned by getting the Regis from Ruby, Sapphire or Emerald, putting them into your party, and traversing the Snowpoint Temple to the bottom.

In Pokémon Diamond, you can obtain Regigigas in Snowpoint Temple but you'll must have Regice, Regirock and Registeel in your Party.

To get these three legendary golems you must migrate them via Pal Park from either Ruby, Sapphire or Emerald.

If you have an Action Replay, you can simply get a cheat that gives you Regigigas:
94000130 FCFF0000
B21C4D28 00000000
B0000004 00000000
10001170 000001E6
D2000000 00000000
Press (R+L)
Now go to the Mining Museum in Oreburgh City and talk to the character who revives fossils (the one behind the counter) and he will have a Regigigas for you at level 20.
Bring Regice, Registeel, and Regirock to the bottom of Snowpoint Temple.

Answer 2

In Pokémon Diamond, you can obtain Regigigas in Snowpoint Temple but you'll must have Regice, Regirock and Registeel in your Party.

To get these three legendary golems you must migrate them via Pal Park from either Ruby, Sapphire or Emerald.

If you have an Action Replay, you can simply get a cheat that gives you Regigigas:

94000130 FCFF0000

B21C4D28 00000000

B0000004 00000000

10001170 000001E6

D2000000 00000000

Press (R+L)

Now go to the Mining Museum in Oreburgh City and talk to the character who revives fossils (the one behind the counter) and he will have a Regigigas for you at level 20.