A new in-game event is underway in Pokemon Go. For the next few days, Niantic is holding Kanto Week, an event celebrating the classic Red and Blue versions with increased spawn rates for some Gen I Pokemon and other bonuses. [Update: Pokemon Go's Kanto Week event is set to end tomorrow, April 17, making this your last opportunity to take advantage of the below bonuses while they're still available.]
Kanto Week runs from now until April 17. For the duration of the event, Kanto-native Pokemon, like the original starting trio Bulbasaur, Charmander, and Squirtle, will appear much more frequently in the wild. Other Gen I monsters, such as Aerodactyl and Snorlax, will also return to Raid Battles.
In addition to that, players will receive double the normal amount of Candy for capturing and transferring Pokemon during Kanto Week. Niantic is also offering special boxes from the in-game store that contain Raid Passes and other helpful items.
Kanto Week ties into the recently added Special Research quest to find Mew. As part of the tasks to encounter the Mythical Pokemon, players need to earn a gold Kanto medal, which is awarded for capturing 100 Pokemon from the region. This event should make it easier to accomplish that feat.
Kanto Week runs through Pokemon Go's next Community Day, which takes place this coming Sunday, April 15. During that event, Eggs will hatch at a quarter of the distance they typically require. Players will also have a greater chance to capture the Electric-type sheep Mareep; if it evolves into Ampharos during the event hours, the Pokemon will learn the powerful Dragon-type attack Dragon Pulse.
Info from Gamespot.com