Pokémon HeartGold and SoulSilver/Nintendo Events
Sinjoh Ruins
This event requires you to have a TRU Arceus acquired with Pokemon Platinum through a WiFi and traded to Pokémon HeartGold and SoulSilver. They are no longer obtainable without trading with another player.
The Sinjoh Ruins are a location in Pokémon HeartGold and SoulSilver. While it is not a part of any known region, it can be visited by way of a mysterious entry point in the Ruins of Alph.
The only known way to the Sinjoh Ruins is by way of the Ruins of Alph. Bringing an Arceus from a Nintendo event here will unlock the new area, but this will only occur if the Arceus is currently the player's partner Pokémon. Cynthia will be found waiting for the player, and will tell them that Arceus has the ability to create newborn Pokémon. She will escort the player into the ruins and show them an area called the Mystri Stage that is linked to Arceus's power of creation. The player will get a choice to obtain only one of either Dialga, Palkia, or Giratina at level 1, equipped with their respective orbs. Arceus must be the only Pokémon in the player's party for this to occur, and a PC is inside the cabin near the ruins for the player to use to deposit all others.
Spikey-eared Pichu
She appears in Pokémon HeartGold and SoulSilver as an event Pokémon obtained in Ilex Forest. She will appear and join the player's party if the Pikachu-colored Pichu is brought to the shrine as the first Pokémon in the party. She has her own unique in-battle and overworld sprites and cannot evolve or be traded outside of HeartGold and SoulSilver. Aside from her unique sprite, moves, and inability to be traded or evolve, she is identical to a normal Pichu in terms of stats. Her maximum stats for the Pokéathlon are different from a regular Pichu. Interestingly, however, her base stats do not differ from a normal Pichu's; the same trend occurs with most other Pokémon with multiple forms which share their base stats, such as Rotom or Arceus. If a Pokémon uses Transform on it, it will have a spiky ear.
Shiny sprites for Spiky-Eared Pichu exist in the coding of the games, although it remains unknown if this special Pichu has the 1 in 8192 chance of being shiny like all other Pokémon encountered in the wild. It is highly likely that the data was only included, as in the case of ???-type Arceus, to prevent the game from crashing if someone was to hack the game, or by default due to every other form difference having both normal and shiny forms despite availability of these Pokémon as shiny.
If taken to Professor Elm, it is revealed that she has traveled through time with Celebi. Elm claims that he and Professor Oak were researching the time travel abilities of Celebi, and claims that this Pichu proves his main theory. He adds that the reason it cannot evolve is because it has been time traveling for so long. He will then call all the Pokémon Center attendants to prevent Spiky-Eared Pichu from being used in trades.
PokéWalker
Trade the GameStop Jirachi to open a new route.
The Nintendo Event April 1st will open a new route
