Update: Bumped to the top. Added more official details via the announcement from Niantic below.
Original: An event focusing on Pokemon GO that focuses on Kanto Pokemon. Kanto starters and Pikachu will appear more often and Snorlax and Aerodactyl are returning as raid bosses.
The appearance of the Mythical Pokémon Mew has attracted Pokémon that were originally discovered in the Kanto region. These classic Pokémon will be seen more frequently starting April 10 at 1 P.M. PDT, so you’ll have the perfect opportunity to earn a gold Kanto medal and even complete your Kanto Pokédex!
What’s more, certain Pokémon such as Aerodactyl and Snorlax will be featured in Raid Battles across the world. Keep an eye out for one you haven’t encountered yet!
As you encounter and catch more Pokémon originally discovered in the Kanto region, all actions will be rewarded with double Candy. So, not only will you be able to catch Pokémon you might not frequently see, but you may also get the chance to register their evolved forms in your Pokédex as well.
During this event, there will also be special boxes containing Raid Passes! These boxes will give you an opportunity to challenge many powerful Pokémon originally discovered in the Kanto region.
This special celebration ends on April 17, so get out there and make some more discoveries. If all goes well, you may be able to finish your first Special Research request and encounter Mew!