Instructions
Travel to the Daycare Center on Island 4. To access Island 4, you must have logged over 60 different breeds of Pokemon into your Pokedex, acquired the National Pokedex from Professor Oak, retrieved the ruby for Celio from Mt. Ember, and defeated the E4 and become the Pokemon Champion.
Breed your Pokemon to get an egg. Using the Daycare Center menu, you must select a male and a female Pokemon from the same egg category. The two Pokemon will create an egg. The time it takes varies and depends upon the number of steps you take. Walk back and forth outside of the pen until the old man inside of the pen walks out of it. The old man leaving the pen signals that the Pokemon have made an egg. Speak to the old man, and he will give you the egg.
Hatch your egg. With the egg in your party menu, travel to Icefall Cave. You must now walk back and forth for 500 to 700 steps. The egg will hatch, and you will have your new baby Pokemon.