Pokemon Y comes with the Pokemon 'Pikachu's ultimate enhancement that replaces it with a the lightning rod Pikachu. It can be obtained by crossing male lightning rod with female Pikachu. To get this done visit Route 5 and visit the Horde. Male lightning rod is located there. Female Pikachu can be brought from Santanule forest, which is located on Route 3. Then, put both of the Pokemon's into care for children and then breed them until you have the egg that you want to get produced.