Shiny Pokémon

Shiny Pokémon are extremely rare Pokémon that differ in coloration from their regular appearance. These color variations may range from minor hue adjustments to completely altered palettes. Only one shiny variation exists for each Pokémon.

In the Map View and tracker, shiny Pokémon are shown in their regular coloration until they appear on the encounter screen or on the summary page, where they have an aura of stars around them and their different coloration is visible.

Once a player captures a shiny Pokémon, their Pokédex will show that they have captured it and additional switch buttons for shiny forms will unlock in each individual Pokédex entry.

List of Shiny Pokémon
Almost all Shiny forms of Pokémon are currently in game data, but only some of them are currently available to obtain by players in gameplay.

History
Shiny Pokémon were released on following days:

2017
March: August: October: December:
 * March, 2017 – The first available Shiny Pokémon in the game – Shiny Magikarp and Gyarados began appearing.
 * It might be reference to original game series as Shiny Gyarados, located at the Lake of Rage, was the Pokémon used to introduce Trainers to shiny Pokémon.
 * August, 2017 – Shiny Pikachu, Raichu and Pichu were released on the first day of the Pokémon GO Park event, in Yokohama, Japan.
 * October, 2017 – Shiny Sableye began appearing on the first day of the Halloween event of 2017.
 * October, 2017 – Shiny Duskull and Dusclops began to appear six days into the event.
 * October, 2017 – Shiny Shuppet and Banette began to appear 11 days into the event.
 * December, 2017 – Shiny Mawile and Absol began being available to catch in Raid Battle Bonus Challange, after main release of Hoenn-region Pokémon.
 * December, 2017 – Shiny Snorunt and Glalie began appearing along with release twenty Water and Ice-type Pokémon from Hoenn region and Delibird.

2018
January: February: March: April: May: June: July: August: September: October: November: December:
 * January, 2018 – Shiny Aron, Lairon and Aggron began appearing along with release of Ground and Rock-type Pokémon from Hoenn region.
 * February, 2018 – Shiny Swablu and Altaria began appearing along with release of Flying and Dragon-type Pokémon from Hoenn region.
 * February, 2018 – Shiny Luvdisc became available to catch in wild with the beginning of the Valentine's Day event.
 * February, 2018 – Shiny Poochyena and Mightyena became available to obtain with the start of Lunar New Year event.
 * February, 2018 – Shiny Dratini, Dragonair and Dragonite began appearing on the February Community Day.
 * March, 2018 – Shiny Lugia was made available to be caught in Raid Battle Bonus Challange with the second temporal release of it as a Legendary Raid Boss.
 * Shiny Lugia is the first Shiny Legendary Pokémon available in the game.
 * March, 2018 – Shiny Magby, Togepi, Wynaut and their families were released with the beginning of the Eggstravaganza.
 * March, 2018 – Shiny Bulbasaur, Ivysaur and Venusaur became available on the March Community Day.
 * March, 2018 – Shiny Murkrow became available to capture with the start of April Fools' Day.
 * April, 2018 – Shiny Mareep, Flaaffy and Ampharos became available on the April Community Day.
 * April, 2018 – Shiny Wailmer and Wailord became available with the start of the Earth Day event.
 * May, 2018 – Shiny Makuhita, Hariyama, Meditite and Medicham became available with the start of the Battle Showdown event.
 * May, 2018 – Shiny Ho-Oh was made available to be caught in Raid Battle Bonus Challenge with the its second temporal release as a Legendary Raid Boss.
 * May, 2018 – Shiny Charmander, Charmeleon and Charizard became available on the May Community Day.
 * May, 2018 – Shiny Omanyte, Omastar, Kabuto, Kabutops and Aerodactyl were released with the start of the Adventure Week event.
 * June, 2018 – Shiny Shellder, Cloyster and Kyogre became available with the beginning of the Water Festival event.
 * June, 2018 – Shiny Larvitar, Pupitar and Tyranitar became available on the June Community Day.
 * June, 2018 – Shiny Roselia was released with the beginning of the Pokémon GO Safari Zone in Dortmund.
 * July, 2018 – Shiny Articuno became available to capture on the Articuno Day mini event.
 * July, 2018 – Shiny Squirtle, Wartortle and Blastoise became available on the July Community Day.
 * July, 2018 – Shiny Plusle and Minun were released with the beginning of the 2018 edition of Pokémon GO Fest.
 * July, 2018 – Shiny Zapdos became available to capture on the Zapdos Day mini event.
 * August, 2018 – Shiny Snubbull, Granbull, Houndour and Houndoom became available.
 * August, 2018 – Shiny Eevee and its branched evolutionary line became available to capture on the August Community Day.
 * August, 2018 – Shiny Natu, Xatu, Sunkern, Sunflora, Pineco and Forretress became available with the start of the Johto Festival.
 * August, 2018 – Shiny Wingull and Pelipper became available with the start of the Safari Zone event in Yokosuka, Japan.
 * September, 2018 – Shiny Growlithe and Arcanine were released to the gameplay.
 * September, 2018 – Shiny Moltres became available to capture on the Moltres Day mini event.
 * September, 2018 – Shiny Geodude, Graveler, Golem, Grimer and Muk became available with the start of Ultra Bonus Event.
 * September, 2018 – Shiny Chikorita, Bayleef and Meganium became available on the September Community Day.
 * October, 2018 – Shiny Krabby and Kingler became available.
 * October, 2018 – Shiny Drowzee and Hypno became available with the start of Psychic Spectacular.
 * October, 2018 – Shiny Nidoran♀, Nidorina and Nidoqueen became a available in celebration of International Day of the Girl Child.
 * October, 2018 – Shiny Shinx, Luxio and Luxray were released.
 * October, 2018 – Shiny Beldum, Metang and Metagross became available on the October Community Day.
 * October, 2018 – Shiny Drifloon and Drifblim became available with the start of Halloween.
 * November, 2018 – Shiny Pinsir was released with the start of Safari Zone in Tainan.
 * November, 2018 – Shiny Caterpie, Metapod and Butterfree became available.
 * November, 2018 – Shiny Gengar became available from Raid Battles during the Special Raid Challenge. After the challenge had ended, Niantic announced that Shiny Gastly became available in the wild.
 * November, 2018 – Shiny Cubone , Marowak, Alolan Marowak , Ponyta and Rapidash became available.
 * November, 2018 – Shiny Budew was released.
 * November, 2018 – Shiny Cyndaquil, Quilava and Typhlosion became available on the November Community Day.
 * November, 2018 – Shiny Elekid and Electabuzz were released with the beginning of Hatchathon. Cross-generation Pokémon Roserade, Honchkrow, Electivire, Magmortar, Togekiss and Dusknoir were released.
 * November, 2018 – Shiny Magnemite and Magneton became available with the start of Let's Go Celebration.
 * November, 2018 – Shiny Alolan Raichu became available.
 * December, 2018 – Shiny Misdreavus and Mismagius became available.
 * December, 2018 – Shiny Sandshrew and Sandslash became available during the Tottori Festival in Japan.
 * December, 2018 – Shiny Azurill, Marill, Azumarill and Delibird became available with the start of Holiday.

Trivia

 * A shiny Pokémon may not appear shiny to nearby Trainers.
 * Shiny Pokémon cannot be batch-transferred, and Trainers will be notified if they try to transfer them.
 * Shiny Pokémon remains shiny after being evolved.
 * Also Pokémon cannot become shiny via evolving non-shiny one.
 * In the main Pokémon series, the Gold and Silver versions were the first games to introduce shiny Pokémon.
 * Unlike the case with seeing regular Pokémon in the Gym, seeing Shiny Pokémon in the Gym for the first time, before capturing them, won't unlock the Pokémon's shiny form switches in Pokédex summary page.
 * There are also no file assets for form switches of only-seen Shiny Pokémon in Pokédex.
 * Registering a shiny Pokémon will also register the non-shiny form to the Pokédex, if the Pokémon was not previously registered.
 * During the Halloween event in 2017, there were shiny forms of Gastly family members added to game data, although they weren't released to be caught in gameplay.
 * Along with each release of selected Pokémon from Hoenn region, there are added to game data all of the sprites for shiny forms of respective Pokémon.
 * Along with releases of new Legendary Raid Bosses, assets for Shiny Forms of these Legendary Pokémon are also added to the game.
 * Shiny Zapdos was temporally available from Raid Battle in 2017 due to game creators' mistake.
 * Between April and, players started noticing that 2D sprites of Kanto- and Johto-region Pokémon had changed, thus they started speculating that during the Kanto Celebration event some or even more of shiny variants of these Kanto Pokémon might be released.
 * Moreover, Reddit user u/Chrales through the data-mining found and revealed that in fact plenty of 2D sprites for shiny variants of Kanto- and Johto-region Pokémon had been added to the game server. However none of these Shiny Pokémon had their in-game 3D models added by that time.
 * Despite all of these 2D sprites of Shiny Pokémon being added to the game, none of Pokémon had their shiny variant released during the Kanto Celebration event.
 * On each Community Day there is significantly higher chance to encounter shiny form of featured Pokémon that generally spawns more often during this event.
 * Research estimates that there was a 1 in 22.7 chance of capturing a Shiny Pikachu during the first Community Day.