Niantic has announced the details for the remaining events for December 2019 from raids to Shadow Pokémon, Legendary Pokémon, or Legendary Shadow Pokémon, to new avatar items, there’s so much to look forward to this Christmas season.

A gift from us to you: Pokémon GO’s December events!

Trainers, While 2019 might be winding down, the world of Pokémon GO never stops! From raids to Pokémon (Shadow Pokémon, Legendary Pokémon, or Legendary Shadow Pokémon!) to new avatar items, there’s so much to look forward to this holiday season. Get cozy, Trainers—it’s going to be a long list full of cool gifts from us to you!

1. A Challenging Development—Team GO Rocket Special Research
2. Different Pokémon will be hatching from Eggs
3. Virizion glides into five-star raids
4. Lugia and Ho-Oh Special Raid Weekend!
5. Pokémon GO Holidays 2019
6. Warm up with a special winter weekend event!

A Challenging Development
Before we get into the jolly announcements—the fight against Team GO Rocket continues! Activate the new Special Research, A Challenging Development, during the month of December to help Professor Willow and the team leaders take down this villainous group. This is another chance to fight Giovanni and save a Legendary Shadow Pokémon you’ve never seen before!

Features

• A Challenging Development, a new Special Research line designed to help take down Team GO Rocket, is available until the end of December.
• Defeat Giovanni this month, and you’ll have a chance to rescue Shadow Zapdos!

Team GO Rocket never rests, Trainers, and neither can we! Be on the lookout for new Team GO Rocket Special Research from Professor Willow every month. For more information, please see our help center article.

All scrambled up! Different Pokémon will be hatching from Eggs!
Starting on Monday, December 16, 2019, you can expect different Pokémon to be hatching from Eggs! Which Pokémon will they be? Incubate some Eggs and start walking to find out!

Virizion glides into five-star raids!
Virizion, the Grassland Pokémon, will be coming to five-star raids! This Grass- and Fighting-type Legendary Pokémon has been said to confound opponents with its swift movements, so make sure you have your battle strategies ready before you encounter it.

Date + Time
Tuesday, December 17, 2019, at 1:00 p.m. PST to Tuesday, January 7, 2020, at 1:00 p.m. PST (GMT −8)

Features

• Virizion will make its debut in five-star raids.

Lugia and Ho-Oh Special Raid Weekend!
Lugia and Ho-Oh return for a Special Raid Weekend! Both the Psychic- and Flying-type Lugia and the Fire- and Flying-type Ho-Oh will be available in Raid Battles! Date + Time Friday, December 20, 2019, at 1:00 p.m. PST to Monday, December 23, 2019, at 1:00 p.m. PST (GMT −8)

Features

• Lugia and Ho-Oh will appear in five-star raids during the event.

Please note that Virizion will still be available in five-star raids during this time.

Pokémon GO Holidays 2019
The Pokémon GO Holidays event is back! Look forward to new Pokémon in costumes, Ice-type Pokémon never before seen in Pokémon GO, event-exclusive Field Research, winter-themed avatar items, and a blizzard full of bonuses!

Date + Time
Tuesday, December 24, 2019, at 12:00 a.m. to Wednesday, January 1, 2020, at 11:59 p.m. in your local time zone

Features

• Pokémon in holiday costumes: Pikachu, Raichu, and Pichu wearing beanies and Stantler wearing bells will appear in Pokémon GO for the first time!
• Pokémon appearing in the wild: Delightful Ice-type Pokémon will be appearing in the wild, such as Sneasel, Delibird, Snorunt, and more! Making its Pokémon GO debut will be Cubchoo, the Chill Pokémon!
• Pokémon appearing in Eggs: Alolan Sandshrew, Alolan Vulpix, Pichu wearing beanies, and Stantler wearing bells will be hatching from 7 km Eggs!
• Pokémon appearing in Raid Battles: Raichu wearing beanies and Stantler wearing bells will be available to challenge in two-star raids!
• Pokémon attracted by Glacial Lure Modules: Throw a Glacial Lure Module onto a PokéStop near you, and you’ll have a chance of encountering Cryogonal, the Crystallizing Pokémon, making its Pokémon GO debut!
• Event-exclusive Field Research: Enjoy event-exclusive Field Research tasks that will reward you with the chance to encounter Pokémon like Pikachu wearing beanies!
• Save Shadow Pokémon! We have reason to believe that Team GO Rocket has turned more Pokémon, including Delibird, into Shadow Pokémon! There might be other Shadow Pokémon to discover in places high and low, so get out there and save them!
• If you’re lucky, you might encounter Shiny Stantler wearing bells and Shiny Snover!
• Winter-themed avatar items coming to the shop! You can look forward to a Stantler Sweater and a Stantler Headband as well as a Beanie Hat to match the one some Pikachu are wearing for this event!

Bonuses
Take note, Trainers! Some bonuses will change throughout the event duration. From Tuesday, December 24, 2019, at 12:00 a.m. to Wednesday, January 1, 2020, at 11:59 p.m. in your local time zone

• Open twice as many Gifts each day: For the duration of the event, the number of Gifts you can open daily will increase to 40.
• Carry twice as many Gifts: For the duration of the event, the number of Gifts you can carry in your inventory will increase to 20.
• One guaranteed single-use Incubator per day: In order to more easily hatch Eggs during the holiday season, Trainers will receive one single-use Incubator at no cost once per day during the event by spinning a Photo Disc on a PokéStop.

From Tuesday, December 24, 2019, at 12:00 a.m. to Wednesday, December 25, 2019, at 11:59 p.m. in your local time zone

• 2× Catch Candy
• 2× Transfer Candy

From Thursday, December 26, 2019, at 12:00 a.m. to Friday, December 27, 2019, at 11:59 p.m. in your local time zone

• 2× Catch Stardust

From Saturday, December 28, 2019, at 12:00 a.m. to Sunday, December 29, 2019, at 11:59 p.m. in your local time zone

• 2× Catch XP

From Monday, December 30, 2019, at 12:00 a.m. to Wednesday, January 1, 2020, at 11:59 p.m. in your local time zone

• 1/2 Hatch Distance when Eggs are placed into Incubators during this time period

Warm up with a special winter weekend event!
During the final Saturday in December (and 2019!), you can look forward to a special eight-hour-long winter weekend event.

Date + Time
Saturday, December 28, 2019, from 11:00 a.m. to 7:00 p.m. in your local time zone

Features

• Two-hour Glacial Lure Module duration: Glacial Lure Modules will last two hours for the duration of the event. Pokémon such as Lapras, Delibird, Cubchoo, and more will be drawn to Glacial Lure Modules during this time!
• Glaceon with Last Resort: Use a Glacial Lure Module to evolve Eevee during the event, and you’ll get a Glaceon that knows the Charged Attack Last Resort.
• Regice returns to raids! Did you miss out on catching a Regice the last time it was available in raids? This is your chance to catch the Iceberg Pokémon!
• Two additional Raid Passes: Receive up to two additional Raid Passes during the special event time period when you spin a Photo Disc at a Gym. These Raid Passes will not be available after the event period is over. You cannot hold more than one Raid Pass at once.

There are just a few weeks left in 2019! Let’s GO end the year strong, Trainers!

Source: https://pokemongolive.com/en/post/holiday2019/