The Seasons Change

Autumn Event was an event in Pokémon GO.

Featured Pokémon
These Pokémon were released with the start of the event:

Autumn-themed Pokémon had increased spawn rates in the wild and from Incense or Lure Modules:

These Shiny Pokémon were released with the start of the event: PS Vulpix PS Ninetales

5-km Eggs obtained during the event would hatch Autumn-themed Pokémon:

The following Raid Bosses were available for a time of this event:

Field Research event tasks
There were several Field Research tasks exclusively for the duration of the event.

Timed Research
During this event there was a Timed Research series that was titled The Seasons Change: Part 1 in game.

Trivia

 * The event time was originally planned to be October 8 a.m. to October  1 p.m., local time. It was modified to be based on PDT due to overlapping with Fashion Week.
 * The 1/4 Egg hatch distance bonus was unannounced in the official blog post.