https://www.gamespot.com/articles/pokemon-go-last-chance-to-hatch-region-exclusive-p/1100-6462160/

Pokemon Go's Ultra Bonus Event has come to an end, but developer Niantic has extended one of the bonuses it offered. The studio announced that Farfetch'd, Kangaskhan, Mr. Mime, and Tauros will continue to hatch from 7 km Eggs until October 8, giving you a little more time to get your hands on these rare Pokemon.

What makes these four monsters particularly desirable is that each one is normally exclusive to a certain region. Tauros can only be found in North America; Mr. Mime only appears throughout Europe; Kangaskhan is primarily found in Australia; and Farfetch'd is limited to Asia.