Holiday

Holiday is a seasonal event in Pokémon GO that takes place in the latter half of December to celebrate real-world Christmas, Hanukkah and the other winter holiday celebrations.

2016 Event
2016 Holiday Event took place from the morning of December, 2016 until noon of January , 2017 (PST).

Features
Each day during the event, trainers were awarded a single-use Egg Incubator when they visited their first PokéStop of the day. There was also a greater chance of obtaining Pokémon Eggs which would hatch Baby Pokémon from Johto region.

Lure modules' duration were also increased up to a whole hour, rather than their normal 30 minutes.

Featured Pokémon
Two weeks prior to this event, on December, 2016, Johto-region Baby Pokémon were released. Reports of Pikachu and Raichu wearing festive hats began to circulate the same day. They were available until the end of this Holiday event,  and any captured would persist in the inventory if not released

Additionally, from the afternoon of December, 2016, through the afternoon of January 2017 (PST), starter Pokémon and their evolved forms were encountered more often.

Shop special offer
During this event there were Holiday Boxes available from the shop for a limited time.

From the morning of December, 2016 through the afternoon of December , 2016 (PST) Special, Great, and Ultra Boxes werer available for purchase from the Shop. These boxes contained some items that are usually not available for purchase and they were offered at a discount rate.

From the afternoon of December, 2016 through the afternoon of January , 2017 (PST) Bronze, Silver, and Gold Boxes were available for purchase. The items in these Boxes included Incense, Lure Modules, Lucky Eggs, Poké Balls, and Great Balls.

2017 Event
2017 Holiday Event took place from the afternoon of December, 2017 and lasted through the afternoon of January , 2018 (PST). Moreover, this event is connected with the release of twenty acquatic-themed, Hoenn-region Pokémon.

Features
Similarly to the year-before event, for the duration of the event, Lure Modules lasted for 6 hours before they expire. and as a special bonus, the first PokéStop visited each day between December, 2017, at 1:00 p.m. (PST) and December , 2017, at 1:00 p.m. (PST) awarded trainers with a single-use Egg Incubator.

Featured Pokémon
Festive Pikachu returned with release of 20 Water and Ice-type Pokémon from the Hoenn region and Johto-region, "present-bearing" Pokémon Delibird. Most of these Pokémon had increased chance to appear in the wild during this event.

Moreover, these Shiny Pokémon were released with the start of the event.

Additionally, during the event there was possibility to hatch Pichu wearing festive hat from 2-km Eggs.

Shop special offer
Year after the very-first special offer boxes, there were new ones for this event, available from the shop for a limited time.

From December through December, 2017 at 1:00 p.m. PST, special boxes featured items such as Super Incubators, Lure Modules and newly introduced Star Pieces.

From December, 2017, at 1:00 p.m. PST through January , 2018, special boxes featured items such as Premium Raid Passes, Super Incubators, and Star Pieces.

This offer introduced new graphic design for such boxes and it differs from previous special offer boxes by having futuristic style with more winter, holiday theme.

Promotional pictures
Following promotional pictures were published by creators of the game across their social media channels.

Trivia

 * Both 2016 and 2017 Holiday events happened to be the last events that occurred in each of years.
 * They're technically also the first events of 2017 and 2018 years respectively, as they both ended in January of following year to that in which they have begun.