Things You'll Need
Instructions
Catch a Ditto on Routes 13, 14, 15 or in the Cerulean Cave. Dittos are relatively uncommon, and the catch rate for a Ditto is about 35 percent.
Put the Pokemon you want to duplicate and Ditto in your team. The Pokemon you want to duplicate must have a gender for the duplication to work.
Take both Pokemon to the Daycare Center on 4 Island and give them to the old Daycare couple.
Wait a few hours and check the Daycare to see if your Pokemon have produced an egg.
Walk or cycle around with the egg on your team and check its status periodically to see how close it is to hatching. Once it hatches, you will have the first stage evolution of whichever Pokemon you put in the Daycare with Ditto.