In 2019, Pokémon GO introduced the concept of Hatch Days. These are days where, for three hours, a certain event exclusive piece of Field Research will be available for players. This research is then forever with the player. Each region has the event at different times. Click the Hatch Day for more details

Azurill DayAzurill Day September 30th 2023 Azurill
Riolu DayRiolu Day July 2023 Riolu