theSLAYER

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

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   Comfey   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   Flower Veil (1) or Triage (2)   Item   None   Bundled Item   None   Card Per Save   Only One Allowed    Moves   (ITALIC means Relearnable)   Celebrate   Leech Seed   Draining Kiss   Magical Leaf   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_1845

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

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.

Across Asia, this gift has been given out as serial code for either ordering or pre-ordering the tickets to M21: The Power of Us.

This gift can be redeemed by US 3DS (regardless of language), EU 3DS (ENG, JPN, KOR, CHS, CHT), JP 3DS and TW 3DS.
This card only comes in Japanese, despite being accessible by those devices.

As of December 1st, it's confirmed that the gifts are receivable in game.
The Taiwanese code card indicates the last day of redemption would be March 31st, 2019.
The redemption dates on the Singaporean code card indicates the event runs from December 8th, 2018 to February 28th, 2019.
It is not clear which end date is the correct one (as both events ARE the same).
     Species   Zeraora   Nickname   (default, save lang)   OT   フウラシティ   TID   180713   Distribution   Serial Code   Location   2018 Pokémon Movie   Dates   (check above)   PID   Cannot Be Shiny   Games   TW & US & EU & JP 3DS: USUM                                                                Lv. 50    Nature   Random   Ability   Volt Absorb (1)   Item   Air Balloon   Bundled Item   None   Card Per Save   Only One Allowed    Moves   (ITALIC means Relearnable)   Plasma Fists   Thunder Punch   Close Combat   Thunder   WC ID 300: 「まぼろしのポケモン　ゼラオラ」's receiving text 0x04 Thank you for coming to see the 2018 Pokémon Movie! Please pick up your gift from the deliveryman in any Pokémon Center.

Wishing まぼろしのポケモン　ゼラオラ こうそくで　いどうする　すがたは
まさに　イナズマのごとし…
プラズマフィストで　しびれる　いちげきを
あいてに　あびせろ！ Format Ver.1.0.6-3, Post Updated Date:20181201_0653

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)

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 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 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.
Igglybuff was added to the shiny pool permanently during the Pokémon GO Eggstravaganza (2019) event.
Wild Jigglypuff and Wigglytuff are not able to spawn shiny in Pokémon Go, meaning the only way to obtain a shiny version of them is to evolve the shiny pre-evolutions.
The event was slated to be between: Apr. 16, 2019, at 1:00 p.m. PDT to Apr. 23, 2019, at 1:00 p.m. PDT (GMT −7)
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.
Cleffa and Smoochum was added to the shiny pool permanently during the Pokémon GO Valentine’s Day Celebration (2019) event.
Wild Jynx, Clefairy and Clefable are not able to spawn shiny in Pokémon Go, meaning the only way to obtain a shiny version of them is to evolve the shiny pre-evolutions.
The event was slated to be between: Feb. 13, 2019, at 1:00 p.m. PST (GMT -8) to Feb. 21, 2019, at 1:00 p.m. PST (GMT -8)
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)