Mythical Pokémon

Mythical Pokémon are group of rare Pokémon which can be encountered by special means, including Special Research, EX Raid Battle and Elite Raid Battle.

In core-series games, Mythical Pokémon are a group of Pokémon seen so rarely in the Pokémon world that some question their very existence.

Characteristics
Mythical Pokémon share the following characteristics:
 * Buddy Pokémon 20 km for 1 candy
 * require 100,000 Stardust and 100 candies to unlock the second Charged Attack
 * can be filtered in Pokémon search by typing mythical
 * if transferable, an extra warning appears when trainers try to transfer them. They also cannot be mass transferred
 * if tradable, require a Special Trade, cost a large amount of Stardust even if already registered by both trainers
 * cannot participate Premier Cup in GO Battle League

Kanto
The Mythical Pokémon from Kanto region is Mew.

Johto
The Mythical Pokémon from Johto region is Celebi.

Hoenn
The Mythical Pokémon from Hoenn region are Jirachi and Deoxys. Deoxys has four different forms.

Sinnoh
There are five Mythical Pokémon from Sinnoh region - Phione, Manaphy, Darkrai, Shaymin and Arceus.

Phione and Manaphy are duo called the Sea Guardians.

Darkai is the part of the Lunar duo along with the Legendary Pokémon Cresselia.

Shaymin has two different forms. It can undergo Form Change.

The last Mythical Pokémon from Sinnoh region is Arceus. It is a trio master of both the Lake Guardians and the Creation Trio. It has 18 different forms corresponding for each of the existing types.

Unova
There are four Mythical Pokémon from Unova region - Victini, Keldeo, Meloetta and Genesect.

Unlike the other Mythical Pokémon's placement in Pokédex, the end of each region of Pokédex, Victini is the first Pokémon in the Unova region Pokédex, even before the Starter Pokémon.

Keldeo is the fourth member of a Legendary Pokémon group called the Swords of Justice. It has two different forms.

Meloetta has two different forms.

The last Mythical Pokémon of Unova region is Genesect, which has five different forms.

Kalos
There are three Mythical Pokémon from the Kalos region - Diancie, Hoopa and Volcanion.

Diancie is the only Mythical Pokémon that can Mega Evolve.

Hoopa has two different forms. It can undergo Form Change.

The last Mythical Pokémon of the Kalos region is Volcanion.

Unknown
Meltan and Melmetal are Mythical Pokémon introduced with Pokémon: Let’s Go, Pikachu! and Pokémon: Let’s Go, Eevee!. It is currently unknown what region they belong to in Pokémon GO. These are the first Mythical Pokémon in the entire franchise to have an evolution line.

Galar
The Mythical Pokémon from Galar region is Zarude.

Trivia

 * Mew, Celebi, Jirachi, Shaymin, Victini, Keldeo and Meloetta have a unique capture mechanic in which the Trainer is given unlimited regular Poké Balls. The first two capture will fail and the third capture will successfully catch the Pokémon. Berries and other types of Poké Balls are unavailable. Some instances also require AR mode. Some instances feature a special background related to that Pokémon.