theSLAYER

This gift was distributed to players who attended the Party of the Decade at Bryant Park, New York, back in 2006,
to commemorate the 10th anniversary of Pokémon (based on the original Japanese release).  
While this gift is similar to the Journey Across America version, with the Original Trainer being 10 ANIV,
the Trainer ID is 06808 (signifying the event date 2006 August 8.) instead of the TID of 00010.

This gift was distributed to players who attended the Party of the Decade at Bryant Park, New York, back in 2006,
to commemorate the 10th anniversary of Pokémon (based on the original Japanese release).  
While this gift is similar to the Journey Across America version, with the Original Trainer being 10 ANIV,
the Trainer ID is 06808 (signifying the event date 2006 August 8.) instead of the TID of 00010.

This gift was distributed to players who attended the Party of the Decade at Bryant Park, New York, back in 2006,
to commemorate the 10th anniversary of Pokémon (based on the original Japanese release).  
While this gift is similar to the Journey Across America version, with the Original Trainer being 10 ANIV,
the Trainer ID is 06808 (signifying the event date 2006 August 8.) instead of the TID of 00010.

This gift was distributed to players who attended the Party of the Decade at Bryant Park, New York, back in 2006,
to commemorate the 10th anniversary of Pokémon (based on the original Japanese release).  
While this gift is similar to the Journey Across America version, with the Original Trainer being 10 ANIV,
the Trainer ID is 06808 (signifying the event date 2006 August 8.) instead of the TID of 00010.

This gift was distributed to players who won a lucky draw, and could redeem it when they attended the SpaceWorld 1999.
Big thanks to @Afepoke for helping us preserve this rare Mew, as well as his other Japanese Gen I files!
 
Original Thread
 

This gift was distributed to players who won a lucky draw, and could redeem it when they attended the SpaceWorld 1997.
Big thanks to @Deoxyz and u/salinbreezy for helping us preserve this rare Mew!

Original Thread
 

This gift was given away to participants of the 2018 International Challenge (November).
Participants were required to take part in at least 3 battles of the Online Competition, with a game synced game and account.
The serial code will then be released to players around 2 weeks after the battles finished, via their PGL account.
As this Online Competition was only available to Ultra Sun and Ultra Moon, the gift is also only receivable on Ultra Sun and Ultra Moon.
   Species   Tapu Lele   Nickname   (default, save lang)   OT   아칼라   TID   181130   Distribution   Serial Code   Location   the PGL   Dates   Dec 18, 2018 
to Jan 31, 2019   PID   Shiny PID   Games   KO 3DS: USUM                                                                Lv. 60    Nature   Random   Ability   Psychic Surge (1)   Item   Psychic Seed   Bundled Item   None   Card Per Save   Only One Allowed    Moves   (ITALIC means Relearnable)   Nature's Madness   Extrasensory   Flatter   Moonblast   WC ID 1633: 「색이 다른 카푸나비나 선물」's receiving text 0x38 This is a gift from the Pokémon Global Link! Please pick up your gift from the deliveryman in any Pokémon Center.

Classic 색이 다른 카푸나비나 선물 인터넷 대회 참가 기념으로
희귀한 색이 다른 카푸나비나를
선물합니다! Format Ver.1.0.6-3, Post Updated Date:20181218_1944

This gift was given away to participants of the 2018 International Challenge (November).
Participants were required to take part in at least 3 battles of the Online Competition, with a game synced game and account.
The serial code will then be released to players around 2 weeks after the battles finished, via their PGL account.
As this Online Competition was only available to Ultra Sun and Ultra Moon, the gift is also only receivable on Ultra Sun and Ultra Moon.
   Species   Tapu Lele   Nickname   (default, save lang)   OT   アーカラ   TID   181130   Distribution   Serial Code   Location   the PGL   Dates   Dec 18, 2018 
to Jan 31, 2019   PID   Shiny PID   Games   JP 3DS: USUM                                                                Lv. 60    Nature   Random   Ability   Psychic Surge (1)   Item   Psychic Seed   Bundled Item   None   Card Per Save   Only One Allowed    Moves   (ITALIC means Relearnable)   Nature's Madness   Extrasensory   Flatter   Moonblast   WC ID 1633: 「いろちがいの　カプ・テテフ　プレゼント」's receiving text 0x38 This is a gift from the Pokémon Global Link! Please pick up your gift from the deliveryman in any Pokémon Center.

Classic いろちがいの　カプ・テテフ　プレゼント インターネットたいかい　さんかきねんに
めずらしい　いろちがいの　カプ・テテフを
プレゼント！ Format Ver.1.0.6-3, Post Updated Date:20181218_1943

This gift was given away to participants of the 2018 International Challenge (November).
Participants were required to take part in at least 3 battles of the Online Competition, with a game synced game and account.
The serial code will then be released to players around 2 weeks after the battles finished, via their PGL account.
As this Online Competition was only available to Ultra Sun and Ultra Moon, the gift is also only receivable on Ultra Sun and Ultra Moon.
   Species   Tapu Lele   Nickname   (default, save lang)   OT   Akala   TID   181130   Distribution   Serial Code   Location   the PGL   Dates   Dec 18, 2018 
to Jan 31, 2019   PID   Shiny PID   Games   US & EU 3DS: USUM                                                                Lv. 60    Nature   Random   Ability   Psychic Surge (1)   Item   Psychic Seed   Bundled Item   None   Card Per Save   Only One Allowed    Moves   (ITALIC means Relearnable)   Nature's Madness   Extrasensory   Flatter   Moonblast   WC ID 1633: 「Tapu Lele variocolor de regalo」's receiving text 0x38 This is a gift from the Pokémon Global Link! Please pick up your gift from the deliveryman in any Pokémon Center.

Classic Tapu Lele variocolor de regalo Aquí tienes tu premio por haber participado
en el Torneo en Línea. ¡Disfruta de este
Tapu Lele variocolor tan especial! Format Ver.1.0.6-3, Post Updated Date:20181218_1941

This gift was given away to participants of the 2018 International Challenge (November).
Participants were required to take part in at least 3 battles of the Online Competition, with a game synced game and account.
The serial code will then be released to players around 2 weeks after the battles finished, via their PGL account.
As this Online Competition was only available to Ultra Sun and Ultra Moon, the gift is also only receivable on Ultra Sun and Ultra Moon.
   Species   Tapu Lele   Nickname   (default, save lang)   OT   Akala   TID   181130   Distribution   Serial Code   Location   the PGL   Dates   Dec 18, 2018 
to Jan 31, 2019   PID   Shiny PID   Games   EU 3DS: USUM                                                                Lv. 60    Nature   Random   Ability   Psychic Surge (1)   Item   Psychic Seed   Bundled Item   None   Card Per Save   Only One Allowed    Moves   (ITALIC means Relearnable)   Nature's Madness   Extrasensory   Flatter   Moonblast   WC ID 1633: 「Un Tapu Lele cromatico in regalo」's receiving text 0x38 This is a gift from the Pokémon Global Link! Please pick up your gift from the deliveryman in any Pokémon Center.

Classic Un Tapu Lele cromatico in regalo Ecco la ricompensa per aver partecipato
alla Gara Online! Divertiti a lottare insieme
a questo rarissimo Tapu Lele cromatico! Format Ver.1.0.6-3, Post Updated Date:20181218_1940

This gift was given away to participants of the 2018 International Challenge (November).
Participants were required to take part in at least 3 battles of the Online Competition, with a game synced game and account.
The serial code will then be released to players around 2 weeks after the battles finished, via their PGL account.
As this Online Competition was only available to Ultra Sun and Ultra Moon, the gift is also only receivable on Ultra Sun and Ultra Moon.
   Species   Tapu Lele   Nickname   (default, save lang)   OT   Akala   TID   181130   Distribution   Serial Code   Location   the PGL   Dates   Dec 18, 2018 
to Jan 31, 2019   PID   Shiny PID   Games   EU 3DS: USUM                                                                Lv. 60    Nature   Random   Ability   Psychic Surge (1)   Item   Psychic Seed   Bundled Item   None   Card Per Save   Only One Allowed    Moves   (ITALIC means Relearnable)   Nature's Madness   Extrasensory   Flatter   Moonblast   WC ID 1633: 「Schillerndes Kapu-Fala als Geschenk」's receiving text 0x38 This is a gift from the Pokémon Global Link! Please pick up your gift from the deliveryman in any Pokémon Center.

Classic Schillerndes Kapu-Fala als Geschenk Hier ist die Belohnung für deine Teilnahme am
letzten Online-Turnier. Viel Spaß mit diesem
seltenen Schillernden Kapu-Fala! Format Ver.1.0.6-3, Post Updated Date:20181218_1939

This gift was given away to participants of the 2018 International Challenge (November).
Participants were required to take part in at least 3 battles of the Online Competition, with a game synced game and account.
The serial code will then be released to players around 2 weeks after the battles finished, via their PGL account.
As this Online Competition was only available to Ultra Sun and Ultra Moon, the gift is also only receivable on Ultra Sun and Ultra Moon.
   Species   Tapu Lele   Nickname   (default, save lang)   OT   Akala   TID   181130   Distribution   Serial Code   Location   the PGL   Dates   Dec 18, 2018 
to Jan 31, 2019   PID   Shiny PID   Games   US & EU 3DS: USUM                                                                Lv. 60    Nature   Random   Ability   Psychic Surge (1)   Item   Psychic Seed   Bundled Item   None   Card Per Save   Only One Allowed    Moves   (ITALIC means Relearnable)   Nature's Madness   Extrasensory   Flatter   Moonblast   WC ID 1633: 「Un Tokopiyon chromatique en cadeau」's receiving text 0x38 This is a gift from the Pokémon Global Link! Please pick up your gift from the deliveryman in any Pokémon Center.

Classic Un Tokopiyon chromatique en cadeau Voici une récompense pour votre récente
participation à la Compétition Internet !
Prenez soin de ce Tokopiyon chromatique rare ! Format Ver.1.0.6-3, Post Updated Date:20181218_1937

This gift was given away to participants of the 2018 International Challenge (November).
Participants were required to take part in at least 3 battles of the Online Competition, with a game synced game and account.
The serial code will then be released to players around 2 weeks after the battles finished, via their PGL account.
As this Online Competition was only available to Ultra Sun and Ultra Moon, the gift is also only receivable on Ultra Sun and Ultra Moon.
   Species   Tapu Lele   Nickname   (default, save lang)   OT   Akala   TID   181130   Distribution   Serial Code   Location   the PGL   Dates   Dec 18, 2018 
to Jan 31, 2019   PID   Shiny PID   Games   US & EU & TW 3DS: USUM                                                                Lv. 60    Nature   Random   Ability   Psychic Surge (1)   Item   Psychic Seed   Bundled Item   None   Card Per Save   Only One Allowed    Moves   (ITALIC means Relearnable)   Nature's Madness   Extrasensory   Flatter   Moonblast   WC ID 1633: 「Shiny Tapu Lele gift」's receiving text 0x38 This is a gift from the Pokémon Global Link! Please pick up your gift from the deliveryman in any Pokémon Center.

Classic Shiny Tapu Lele gift Here is your reward for your
participation in the recent
Online Competition!
Enjoy this rare Shiny Tapu Lele! Format Ver.1.0.6-3, Post Updated Date:20181218_1427

On the official page for Birthday promotions, the 2nd Birthday distribution was supposed to end right before Let's Go Pikachu & Eevee launches,
and the birthday giveaway would then only be the Chansey Gift for those games.

However, either due to oversight or perhaps a secret distribution only for those who ask for the 3DS versions of the birthday gift,
this 3rd distribution was given away only at select Pokémon Centers, provided the staff doesn't claim that such a distribution doesn't exist.
It's also possible before mid-November ended (the transition to Let's Go), staff gave away this event instead of the 2nd distribution.

In any case, some people managed to get this rare card. It is still required for players to be in their birthday month to receive this.
Identification would have to be presented upon redemption, and travelers can do so by showing their passport.
     Species   Pikachu   Nickname   (default, save lang)   OT   ポケセン♪   TID   181101   Distribution   Infrared   Location   a Pokémon Center   Dates   Nov 01, 2018 to ?   PID   Cannot Be Shiny   Games   All Regions 3DS: SM USUM                                                                Lv. 10    Nature   Jolly   Ability   Static (1)   Item   None   Bundled Item   None   Card Per Save   Only One Allowed    Moves   (ITALIC means Relearnable)   Celebrate   Growl   Play Nice   Quick Attack   WC ID 301: 「おたんじょうび　おめでとう！」's receiving text 0x08 Thank you for coming to the Pokémon Center! Please pick up your gift from the deliveryman in the game.

Birthday おたんじょうび　おめでとう！ ポケモンセンターから
おたんじょうびの　おいわいに
とっても　すてきな　ポケモンを
プレゼントするよ！ Format Ver.1.0.6-3, Post Updated Date:20181217_1833

On the official page for Birthday promotions, the 2nd Birthday distribution was supposed to end right before Let's Go Pikachu & Eevee launches,
and the birthday giveaway would then only be the Chansey Gift for those games.

However, either due to an oversight or perhaps a secret distribution only for those who ask for the 3DS versions of the birthday gift,
this 3rd distribution was given away only at select Pokémon Centers, provided the staff doesn't claim that such a distribution doesn't exist.
It's also possible before mid-November ended (the transition to Let's Go), staff gave away this event instead of the 2nd distribution.

In any case, some people managed to get this rare card. It was still required for players to be in their birthday month to receive this.
Identification would have to be presented upon redemption, and travelers can do so by showing their passport.
     Species   Eevee   Nickname   (default, save lang)   OT   ポケセン♪   TID   181101   Distribution   Infrared   Location   a Pokémon Center   Dates   Nov 01, 2018 to ?   PID   Cannot Be Shiny   Games   All Regions 3DS: SM USUM                                                                Lv. 10    Nature   Jolly   Ability   Run Away (1) 
or Adaptability (2)   Item   None   Bundled Item   None   Card Per Save   Only One Allowed    Moves   (ITALIC means Relearnable)   Celebrate   Sand Attack   Baby-Doll Eyes   (None)   WC ID 301: 「おたんじょうび　おめでとう！」's receiving text 0x08 Thank you for coming to the Pokémon Center! Please pick up your gift from the deliveryman in the game.

Birthday おたんじょうび　おめでとう！ ポケモンセンターから
おたんじょうびの　おいわいに
とっても　すてきな　ポケモンを
プレゼントするよ！ Format Ver.1.0.6-3, Post Updated Date:20181217_1852

A rudimentary viewer and editor program for GP1 files.
Supports drag and drop (just drag the GP1 onto the program).

Has a function to store location data, as well as use stored location data.
The bundled location.txt needs to be in the same folder as the program, for it to work.
Also has in-built CP calculator, based on IVs and level.
Note: the CP shown, is based on PGo CP calculation, which is how Go Park works.
Initial encounter, it will show PGo details. Once captured, the CP gets rerolled to Let's Go CP.

If you're rehosting it, please link/source THIS page.
Source Code: https://github.com/PP-theSLAYER/gp1editor
(I gotta warn you, it's horrible code)

Note from 13th December, 2018:
On this day, some of the stats of certain Pokemon has been changed.
If I'm not mistaken, unlike the forced stat change enforced during Let's Go's release, these only kick in if:
(1) you evolved into that Pokemon after the change or
(2) you powered up the particular species after the change or
(3) you freshly captured that species after the change or
(4) you received the Pokemon from trade after the change.
Meaning if you already had the creature before the change, it's CP and stats will remain unchanged on Pokemon Go, until you performed one of the points above.
Do note that these changes could be enforced in the future, even if the actions specified above wasn't performed.
[Confirmed on my end; I transferred 2 Meltan on 13-Dec, one captured before and one captured after the change.
The older one uses old CP calculation, while newer one uses new calculation. See image in screenshots section]

 In any case, these are the Pokemon affected by the change:
 

Disclaimer:
THIS POKEMON WILL NOT BE LEGAL WITH ANY VIRTUAL CONSOLE RELEASE
(AND BY EXTENSION, CANNOT BE SENT TO GEN 7 AND ONWARD).

Original Thread:
 

Original Description:
In the Fall of 1998 Nintendo Power held a contest to “Win Mew for your Pokémon collection!” 151 winners of this contest would be given the chance to mail their cartridge into the Nintendo Power Headquarters and receive it back with a brand-new mew on their game save. Contest winners were notified by mail by 2/28/1999 that they had won the contest, making this the earliest known Mew distribution in the west.
More can be read on the original thread.

Disclaimer:
THIS POKEMON WILL NOT BE LEGAL WITH ANY VIRTUAL CONSOLE RELEASE
(AND BY EXTENSION, CANNOT BE SENT TO GEN 7 AND ONWARD).

Credits:
@Gridelin, @suloku and /u/Th4tGuyUKn0
 
Original Thread:
 

In these games, Dragonair has a 1% appearance rate on the waters of Route 10.

This entry was transferred from from Pokémon Go to Let's Go Pikachu and Lets Go Eevee.
The Original Trainer for Pokémon Go was changed for privacy purposes.

As part of the rewards for players taking part in the Niantic's Earth Day 2019, Diglett was added to the shiny pool permanently.
Also part of the event's reward, Diglett spawns were common, which lasted between April 29th (1PM PDT) till May 2 (1PM PDT).
This page holds a GP1 format (to be inserted into Go Park using PKHeX, or dragged to the left side of PKHeX and converted in .PB7)

This entry was transferred from from Pokémon Go to Let's Go Pikachu and Lets Go Eevee.
The Original Trainer for Pokémon Go was changed for privacy purposes.
This page holds a PB7 format (already captured Pokémon) and a GP1 format (to be inserted into Go Park using PKHeX)

This entry was transferred from from Pokémon Go to Let's Go Pikachu and Lets Go Eevee.
The Original Trainer for Pokémon Go was changed for privacy purposes.
This page holds a PB7 format (already captured Pokémon) and a GP1 format (to be inserted into Go Park using PKHeX)

This entry was transferred from from Pokémon Go to Let's Go Pikachu and Lets Go Eevee.
The Original Trainer for Pokémon Go was changed for privacy purposes.
This page holds a PB7 format (already captured Pokémon) and a GP1 format (to be inserted into Go Park using PKHeX)

This entry was transferred from from Pokémon Go to Let's Go Pikachu and Lets Go Eevee.
The Original Trainer for Pokémon Go was changed for privacy purposes.
This page holds a PB7 format (already captured Pokémon) and a GP1 format (to be inserted into Go Park using PKHeX)

This entry was transferred from from Pokémon Go to Let's Go Pikachu and Lets Go Eevee.
The Original Trainer for Pokémon Go was changed for privacy purposes.
This page holds a PB7 format (already captured Pokémon) and a GP1 format (to be inserted into Go Park using PKHeX)