There are two ways of getting Groudon on Pokemon Diamond. The First way is trade it with people in the GTS (Global Trade Station). Or you can migrate it from Pokemon Emerald, Ruby, or Sapphire.
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if you have action replay you will get to pick a pokemon so groudon is a hard pokemon you need the red orb for groudon on pokemon soul silver version or pokemon heart gold version but use action replay on pokemon pearl,diamond,platinum
In Diamond & Pearl? Impossible without migrating, trading, or Action Replaying.
I use Ho-oh arceus darkrai jirachi groudon and deoxys
Yes, You can catch Groudon in Pokemon Emerald.
kYOGRE AND GROUDON ARE IN POKEMON MOVIE UR MOTHER