Other than catching Pokemon at random, the best way to get one is by hatching eggs in Pokemon Go. Hatching is done by walking in real life. In order to get your egg ready, you must walk a certain amount of kilometers.
The only problem with this idea is uncertainty. Until the egg hatches, you have no idea what’s inside it. It may be a somewhat rare or just another Pidgey Pokemon. At first, it was hard to guess whether the Pokemon are given at random or is there any process behind it. As more and more players started playing, there is now a sufficient amount of data to guess which Pokemon are the most and least common.
Nether Fable, a website gathering data via user feedbacks has compiled a useful information on this topic. It reveals for 2km eggs, Weedle is the most commonly received Pokemon, followed by Pidgey and Caterpie. Clefairy falls in the rarest category with just around 1 percent users getting a hang of it.
For the 5km eggs, the most common Pokemon is Pontya, even though it is still only present in about five percent of 5km eggs. The rarest is Koffing with just 0.3% showing.
Last, the 10km category has Eevee as the most common Pokemon with over 17% births. The least common Pokemon varies with region and includes Kangaskhan, Tauros, Farfetch’d & Mr. Mime.
Following is the full list of egg hatching possibilities in Pokemon Go
For 2Km Eggs
For 5Km Eggs
For 10Km Eggs