https://www.polygon.com/2018/3/26/17163838/pokemon-go-mew-daily-quests-update

Mythical monster Mew arrives in Pokémon Go this week, Niantic announced, coinciding with a feature-heavy update to the mobile game.

Unlocking and capturing Mew, the rare, 151st Pokémon, is tied to completing several story-based tasks. Guided by the game’s resident scholar Professor Willow, the new Field Research and Special Research quests will give players new incentive to check in daily — as well as a new way to capture Pokémon.