What is Swarming Mimikyu?
Swarming Mimikyu was a special Halloween event, introduced on Halloween 2018. The challenge was to capture as many swarming Mimikyu as you can by the end of the time limit. The event lasted for the entirety of Halloween, from 12 am on 31st October, 2018 to 12 am on 1st November, 2018.
During the event, escaped Mimikyu randomly appeared on pages of the RPG. Upon spotting one, you can click the image. A page appears with a captcha code. After entering the correct code, the Mimikyu is logged as being caught by you. Rankings can be checked along with the number of Mimikyu logged under the Swarming Pokémon tab in Challenges.
The Mimikyu will look like this: 
Prizes were distributed based on the rankings at 12 am on 1st November, 2018.