What is Swarming Bunnelby?
Swarming Bunnelby is a special Easter event, first introduced in Easter of 2017. The challenge was to capture as many swarming Bunnelby as you can by the end of the time limit. The event lasts for the entirety of the Easter weekend, from 12 am Saturday to 12 am Monday.
Swarming Bunnelby replaced the defunct Buneary Madness event, which was last held in 2014.
During the event, escaped Bunnelby randomly appear on pages of the RPG. If you spot one, you can click the image. A page appears with a captcha code. After entering the correct code, the Bunnelby is logged as being caught by you. Rankings can be checked along with the number of Bunnelby logged under the Swarming Pokémon tab in Challenges.
The Bunnelby will look like this: 
Prizes are distributed based on the rankings at 12 am on Sunday & Monday.
For Easter 2017, the event was held twice over 2 weekends. The grand prize for both weekends was a GoldenBunnelby, and the top 10 won a ShinyBunnelby in the first weekend, with the top 10 for the following weekend winning a DarkBunnelby.
For Easter 2018, the event was held twice over 1 weekend. The grand prize for both the days was a GoldenBunnelby, and the top 10 won a ShinyBunnelby on Saturday, with the top 10 for Sunday winning a DarkBunnelby.
ToxiCity for the image.