Event

Events celebrate a special occasion and offer rewards for trainers. These events usually last about a week and grant trainers a chance to complete their Pokédex by increasing the chance of acquiring rare Pokémon. Trainers may also see an increase in Pokémon spawns and receive more Items, XP, Stardust, and Candy.

Halloween
This event took place between October 26th to November 1st.

Trainers received double Candy for catching, hatching, and transferring Pokémon. The required Buddy distance was reduced by a quarter. This meant that Pokémon received Candy four times faster.

Trainers saw an increased spawn rate for scary Pokémon. These Pokémon included: Zubat, Golbat, Gastly, Haunter, Gengar, Drowzee, Hypno, Cubone, and Marowak.

Daily Bonus Celebration
This event took place between November 7th to November 11th.

To celebrate the new Daily Bonus feature, more Pokémon spawned and PokéStops granted more items.

Thanksgiving
This event took place between November 23rd to November 30th.

As a thank you to the community, Niantic rewarded trainers with double XP and Stardust.

It was also confirmed that trainers received four times the amount of XP when they used a Lucky Egg during the event.

Holiday
This event took place beginning on the morning of December 25th 2016 and went until noon (PST) on January 3rd 2017.

Each day during the event, trainers were awarded a single-use Incubator when they visited their first PokéStop of the day. There was also a greater chance of obtaining Eggs which would hatch Gen II baby Pokémon.

From the morning of December 25th through the afternoon of December 30th (PST), Special, Great, and Ultra Boxes were available for purchase from the Shop. These boxes contained items that were usually not available for purchase and they were offered at a discounted rate. In addition, from the afternoon of December 30th through the afternoon of January 3th (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.

Two weeks prior to this event, on December 12th, Gen II Pokemon began appearing in eggs. Reports of Pikachu and Raichu — donned with Festive hats — began to circulate the same day of the release of the second generation. They were available until the end of the Holiday event,  and any captured would persist in the inventory if not released

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

Valentine's Day
This event took place between February 8th and February 15th, 2017.

Trainers were awarded double Candy every time they caught, hatched, and transfered Pokémon. Buddy Pokémon also found candy twice as fast.

Trainers noticed an increased spawn rate of Chansey, Clefable, and many other adorable pink Pokémon. Cleffa, Igglybuff, and Smoochum were also be more likely to hatch from Eggs.

Additionally, lure modules' duration were increased up to six hours, rather than their normal 30 minutes. After the event concluded, lures continued to last 6 hours until 4pm PST on Saturday, February 18th.

Confirmed Pokémon
The following Pokémon had been confirmed to have increased spawn rates, according a various Trainers around the world.

Wild Pokémon

Egg Pokémon

Pokémon Day
This event took place between February 26th and March 6th, 2017.

To celebrate Pokémon Day, any Pikachu that were encountered in the wild wore a festive party hat. Any Pikachu captured during the event will keep its hat forever.

Water Festival
This event takes place between March 22nd and March 29th, 2017.

There will be an increased frequency of Water-type Pokémon encounters. Pokémon like Magikarp, Squirtle, Totodile and even the elusive Lapras will be easier to find in the wild. There is also a higher chance to encounter Johto Pokémon in water biomes.