Instructions
Select a female Pikachu or Raichu who is holding a Light Ball to mate with any Pokemon in the same egg group. Alternatively, select a Pikachu or Raichu of either gender who is holding a Light Ball to mate with a Ditto.
Put the Pokemon into the Pokemon Day Care on Route 34 in Johto.
Continue with your training and adventures until the old man who runs the Pokemon Day Care calls you through the Pokegear device to alert you that the female Pokemon has laid an egg.
Return to the Pokemon Day Care to receive the egg. When the egg hatches, the newborn Pichu will possess the Volt Tackle move.