You can get a Spiky-eared Pichu in Pokémon HeartGold and SoulSilver if you get the movie-event Pikachu-colored Pichu and bring it to Celebi's Shrine in Ilex Forest in HeartGold or SoulSilver.
no
No, that is only avilable for Pokemon HeartGold and SoulSilver. But a Shiny Pichu can be obtained in any game with Pichu in it, but it's really hard to find.
no
Yes, you can catch the Spiky-eared Pichu in the English versions of Pokémon HeartGold and SoulSilver however you need access to the Gamestop or Wi-Fi Pikachu-colored Pichu distribution in order to gain access to the Spiky-eared Pichu.
Action replay or Nintendo events
No, not anymore. They are done with doing events for Pokemon HeartGold and SoulSilver.
its impossible unless you trade it from heartgold or soulsilver after the Wi- Fi event
The notched ear pichu is only available on Pokemon heartgold and soulsilver. Source: http://bulbapedia.bulbagarden.net/wiki/Notched_ear_pichu
No, infact the game has a pervention method to pervent a Shiny Notched Ear Pichu from being shiny.
The difference is that the pikachu-colored pichu is the event pichu forDPPt, whereas the notched ear pichu is the pichu that joins your party one you transfer it to HeartGold or SoulSilver (In the Ilya forest).
you find it at viridian forest