2. Tauros, Farfetchd, Kangaskhan, Mr. Mime
These are the region-specific Pokémon. Tauros can only be found in the wild in North America, Kangaskhan in Australia and the Pacific Islands, Mr. Mime in Europe, and Farfetchd in Asia. They can be hatched from 5km eggs, but with so many Pokémon in the 5km category, it will take some work.
1. Mew, Mewtwo, Articuno, Zapdos, Moltres, Ditto
These "legendaries" (except Ditto) are, according to Ali, yet to be found by any user on Pokémon Go, but could be coming soon.
This list should cause no shortage of people with some differing opinions. Maybe Aerodactyl should be here, or maybe you were one of the people losing your god damn mind over a Vaporeon in Central Park. No matter what, if you've got a handful of these you should, ahem, count yourself lucky.