Two weeks prior to this event, on December 12th, 2016, Johto-region Baby Pokémon were released. Pikachu and Raichu wearing festive hats began to appear the same day. They were available until the end of this Holiday event, and any captured would persist in the inventory if not transferred. 
From the afternoon of December 30th, 2016, through the afternoon of January 8th 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 25th, 2016 through the afternoon of December 30th, 2016 (PST) Special, Great, and Ultra Boxes were 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 30th, 2016 through the afternoon of January 3rd, 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. 
Following promotional pictures were published by creators of the game across their social media channels.
- The holiday season has arrived! Celebrate it with us!. Pokémon GO Live. Retrieved on 2016-12-23.
- More Pokémon and a limited edition Pikachu are coming to Pokémon GO. Pokémon GO Live. Retrieved on 2016-12-19.
- Holiday Q&A. G+ post. Retrieved on 2017-03-22.
- Limited-time holiday item packs!. Pokémon GO Live. Retrieved on 2016-12-25.
- Gift Box tiers and included items.. /r/TheSilphRoad. Retrieved on 2018-12-17.
- Contents of Gift Boxes, Phase 2. /r/TheSilphRoad. Retrieved on 2018-12-17.