Like Pokémon Platinum, Heart Gold & Soul Silver have special details implemented within the game if you send certain Pokémon over. With this Pokémon, the Movie 12 Arceus (and other subsequent Arceus from various events around the world), you get new aspects in both Platinum and Heart Gold & Soul Silver. The special feature in this game for Arceus is much more elaborate than the Platinum one.

If you trade Arceus over to Heart Gold & Soul Silver from Diamond, Pearl or Platinum and take the Arceus with you to the Ruins of Alph to later activate the special Sinjoh Ruins, you will meet up with Cynthia, the former Champion of the Sinnoh Region.

She will explain that Arceus has the ability to create newborn Pokémon. Out of the three possibilities, you only have the option of getting one so you have to choose wisely. They are all at Level 1 so it is a truely personal preference based decision and they all have moves in their movepool when they level up they don't normally know.

Dialga
Dialga
Level 1
OT: Yours Trainer Memo:
??? Nature.
Date of Obtaining
Obtained at Sinjoh Ruins. Met at Level 1
Attacks:
Dragonbreath
Scary Face
 
 
ID No: Yours
Hold Item:
Adamant Orb
Palkia
Palkia
Level 1
OT: Yours Trainer Memo:
??? Nature.
Date of Obtaining
Obtained at Sinjoh Ruins. Met at Level 1
Attacks:
Dragonbreath
Scary Face
 
 
ID No: Yours
Hold Item:
Lustrous Orb
Giratina
Giratina
Level 1
OT: Yours Trainer Memo:
??? Nature.
Date of Obtaining
Obtained at Sinjoh Ruins. Met at Level 1
Attacks:
Dragonbreath
Scary Face
 
 
ID No: Yours
Hold Item:
Griseous Orb
 
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