Pokémon Go: This is the Halloween event
This October Halloween is celebrated. This year, Pokémon Go will also celebrate with various costumed Pokémon and special events.
It's October, and that means that even if it's Halloween only on the 31st, many people are already enjoying it even though there are more than two weeks left. It is common for games as a service to celebrate it and Pokémon Go will not miss the appointment. He has already announced and given details of this year's Halloween event.
Halloween in Pokémon Go
We will be able to rescue more dark Pokémon from Team GO Rocket. Prepare to rescue the following Pokémon from Team GO Rocket Recruits at nearby PokéStops: Weedle, Kakuna, Beedrill, Electabuzz, Magmar, Lapras, Mareep, Seedot, Nuzleaf, Sableye, Trapinch, Cacnea, Shuppet, and Duskull. There will also be new clothes in the Fashion Shop for our avatar, such as a Zubat backpack, a Pikachu jumpsuit, a Cubone or Litwick cap, and a Mimikyu backpack. Halloween in Pokémon Go will celebrate the debut of a spooky Shiny Pokémon: with a bit of luck, we may find a Shiny Yamask.
The special Halloween event in Pokémon Go begins on Thursday, October 17, 2019 at 22:00 p.m. CEST and ends on Friday, November 1, 2019 at 22:00 p.m. CEST. During this time, more Ghost and Dark-type Pokémon will appear in the wild, in Eggs and raids: Gastly, Murkrow, and many more. Yamask, the Spirit Pokémon, makes its debut at this event. There will also be Pokémon in cute and scary Halloween costumes in raids and in the wild, with Bulbasaur dressed up as Shedinja, Charmander from Cubone and Squirtle from Yamask in raids, while there will be Pikachu in wild form dressed up as Mimikyu, and all. These Pokémon may be Shiny. Lastly, Darkrai will appear in the five-star raids.
There will be fun and terrifying field research assignments for a limited period of time throughout this event. Coaches will receive a message and will have to refer to our special investigation when the Halloween event begins. In the official announcement they say that we may meet a Forbidden Pokémon. They will also give us, during the time of this Halloween event, double the Candy per capture, per hatch and per transfer.
Source: Official Pokémon Go blog



