If you bring a Pikachu-colored Pichu from the Mystery Gift Event (Not obtainable, you'll need the Action Replay to get it now.), bring it to the Shrine and Spiky-Eared Pichu will appear from behind the Shrine.
ilex forest shrine
Go to the shrine on ilex forest. Talk to it!
The note in the Ilex forest is towards the beginning of the forest. It is next to the Celebi shrine. You will most likely need cut to access the note and shrine, though.
take the GS ball to the shrine in ilex forest
Ilex forest
ilex forest
Celebi is found in the Ilex forest near the 2nd Gym, at the shrine
to Goldenrod city if your in pokemon silver
a guy in the ilex forest
Go to a shrine in Ilex forest and after that you time travel
you go in the Ilex forest
You must have the pichu from gamestop, and take it to the shrine in the ilex forest.