The spiky ear pichu is an event Pokemon you can get in Heart Gold and Soul Silver.
It has a different sprite and everything, comes female at level 30 (holding zap plate) and comes with the moves Volt tackle, helping hand, swagger, and pain split.
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. You can't transfer it to other games either.