Events

Events are either in-game or both in-game and real-world celebrations for special occasions. Events can last one day or several weeks and grant trainers a chance to complete their Pokédex by increasing the chance of acquiring rare or special Pokémon.

During them, there are various temporal changes to the game that can be applied (bonuses and perks for trainers) such as:
 * Specific Pokémon spawn increased.
 * Specific Pokémon in Eggs, Raid Battles and in temporary Research tasks.
 * Specific Pokémon wearing event-themed hats.
 * Extended duration of Star Piece, Lucky Egg, Lure Modules and Incense.
 * Increase of Incubator efficiency.
 * Reduced buddy distance and trading or evolving cost.
 * Multiplied Stardust, Candy and XP for several actions such as hatch, catch, transfer, evolving and battling.
 * Release of specific Pokémon species, forms and shiny forms.
 * Release of Special Research tasks.
 * Special shop offer.
 * Specific attacks.

There are three major kinds of events:
 * Unique events: events that happened only once.
 * Seasonal events: events that happened more than once. Normally, these events are related to holidays and they do not tend to happen more than once a year.
 * Recurring events: events that happened more than once but are neither seasonal (?) nor related to special occasions.

Moreover, some events are worldwide available, while others can happen in a specific region. For instance, some events happened only on Europe, while others happened only on Japan.

Sometimes events can be also ticketed for an access to all its features and bonuses.

Unique and seasonal events
Below there are all seasonal and unique events listed by each year.

2016
There were 5 events during 2016, 1 of them was regional event.

2017
There were 23 events during 2017, 11 of them were regional events.

2018
There were 31 events during 2018, 4 of them were regional events.

2019
There were 39 events during 2019.

2020
So far there were 26 events during 2020.

Recurring events
There are plenty of events that happen to reoccur either regularly or not. They differ from seasonal events as they may occur more than once in the same year.

Event Pokémon
Event Pokémon are Pokémon that have unique accessories or clothing such at hats, glasses or scarves and can only be obtained during an special event. They cannot be mass-transferred, similar to Legendary, Mythical, or Shiny Pokémon. They usually do not appear in the Pokédex, because they are not handled as forms.