It's a glitch within Pokemon Soul Silver(it may be in Heart Gold too but I can't confirm it since I don't have that version of the game). Spiky-Ear Pichu is a gift given out to movie-goers who bought tickets to see the Pokemon Arceus movie. But its sprite data, as with other promo Pokemon, is already hidden inside the game. And this glitch lets you see the sprite. Here's what happened. I participated in the Pokethlon Technique course with a regular Pichu, and I won. Pichu gets a Technique medal. In the 'Shinrai' room of the Pokethlon Museum(2nd room), all the medals you earned with the different species of Pokemon are recorded there. Strangely enough, the Pichu sprite in that room was not a regular Pichu, but the Spiky-eared variant. I'll take a picture of it when I get my digital camera. I never owned a spiky-eared Pichu and probably never will, but it's still quite a fun glitch.