theSLAYER

As part of the Let's Go Pikachu promotion worldwide (except Korea), various Cap Pikachu were given away to players via the common code.
The common code for Sinnoh Cap Pikachu is "LETSGOPIKACHU09".
These codes worked for US, EU, JP and TW versions of the 3DS console.
For the JP and TW versions, they can only receive the English version of the wonder card, regardless of language they're playing on.
     Species   Sinnoh Cap Pikachu   Nickname   (default, save lang)   OT   Ash   TID   060407   Distribution   Serial Code   Location   a lovely place   Dates   Nov 09 to Dec 01, 2018   PID   Cannot Be Shiny   Games   US & EU & JP 3DS: USUM                                                                Lv. 9    Nature   Hardy   Ability   Static (1)   Item   None   Bundled Item   None   Card Per Save   Only One Allowed    Moves   (ITALIC means Relearnable)   Thunderbolt   Quick Attack   Iron Tail   Volt Tackle   WC ID 1629: 「Ash's Pikachu (Sinnoh Cap)」's receiving text 0x2C Thank you for playing Pokémon! Please pick up your gift from the deliveryman in any Pokémon Center.

Wishing Ash's Pikachu (Sinnoh Cap) Ash and Pikachu encounter
a harsh rival upon arriving in Sinnoh.
While they get off to a rocky start,
they break through with
steadfast determination. Format Ver.1.0.6-3, Post Updated Date:20181110_0048

This event was distributed to players at Pokemon Centers in Japan via Local Wireless,
to celebrate the annual Tanabata Festival.
 
 Species   Jirachi   Nickname   (default, save lang)   OT   たなばた   TID   08014   Distribution   Local Wireless   Location   PC Tohoku   Dates   Aug 01 to 31, 2014   PID   Shiny PID   Games   All Regions 3DS: XY    Lv. 10      Nature   Random   Ability   Serene Grace (1)   Item   Star Piece 
Classic   Moves   (ITALIC means Relearnable)   Wish   Swift   Healing Wish   Moonblast   WC ID 34: 「いろちがいの　ジラーチ　プレゼント」's receiving text  0x51 Thank you for coming to the Pokémon Center Tohoku! Please pick up your gift from the delivery girl in the game. いろちがいの　ジラーチ　プレゼント ポケモンセンタートウホクに
あそびに　きてくれて　ありがとう！
たなばたを　イメージした
わざを　おぼえた
とても　めずらしい　いろちがいの
ジラーチを　プレゼント！

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.
Redemption was noted to have began on November 12th, 2018.
The end date slightly differed between SG and TW pamphlets, even though it's technically the same event.
     Species   Lugia   Nickname   (default, save lang)   OT   フウラシティ   TID   180413   Distribution   Serial Code   Location   2018 Pokémon Movie   Dates   (check above)   PID   Cannot Be Shiny   Games   TW & US & EU & JP 3DS: SM USUM                                                                Lv. 100    Nature   Random   Ability   Multiscale (HA)   Item   None   Bundled Item   None   Card Per Save   Multiples Allowed    Moves   (ITALIC means Relearnable)   Aeroblast   Hurricane   Defog   Tailwind   WC ID 299: 「かぜのルギア　プレゼント」'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 かぜのルギア　プレゼント いちねんに　いちど
かぜまつりのひに　あらわれる
でんせつのポケモン　ルギア
おおきな　つばさを　はばたかせ
きょうりょくな　かぜを　くりだす！ Format Ver.1.0.6-3, Post Updated Date:20181115_0013

This event is the Singapore Garchomp, serial code only redeemable on US 3DS.
 
Distribution Title A Special Garchomp! Wondercard ID 17     PID Cannot Be Shiny     Games XY Type Serial Code Dates Jan 24 - Mar 31 2014 Species Garchomp Nickname (default) Gender Male Level 48 Nature Random Ability Sand Veil (1) OT XY TID 1244 Location a lovely place Ribbon Classic Ball Cherish Ball Held Item None Moves Draco Meteor Dragon Claw Dig Crunch Relearn
Moves (None) (None) (None) (None) Receiving Text 0x35 Thank you for receiving this distribution! Please pick up your gift from the delivery girl in any Pokémon Center.

In Pokemon Diamond, Pearl and Platinum Versions, holds the event location Newmoon Island.

After using the event item Member Card, players gain access to the defunct Harbor Inn in Canalave City,
falls asleep enters a "dream state", dreaming of an encounter with Darkrai at Newmoon Island.
Darkrai can be captured in the "dream". If defeated or fled from, it can be re-battled again in the actual location.
The Member Card event key item was only distributed to Pokemon Platinum.
     Species   Darkrai   Nickname   (default, save lang)   OT   (recipient)   TID   (recipient)   Distribution   In-Game Encounter   Location   Newmoon Island   Dates   (Various)   PID   Chance of Shiny   Games   Platinum                                                                Lv. 50    Nature   Random   Ability   Bad Dreams   Item   None    Moves       Hypnosis   Feint Attack   Nightmare   Double Team
  Format Ver.1.0.6-2, Post Updated Date:20180508_0013

As part of the Let's Go Pikachu promotion worldwide (except Korea), various Cap Pikachu were given away to players via the common code.
The common code for Hoenn Cap Pikachu is "LETSGOPIKACHU06".
These codes worked for US, EU, JP and TW versions of the 3DS console.
For the JP and TW versions, they can only receive the English version of the wonder card, regardless of language they're playing on.
     Species   Hoenn Cap Pikachu   Nickname   (default, save lang)   OT   Ash   TID   091303   Distribution   Serial Code   Location   a lovely place   Dates   Nov 09 to Dec 01, 2018   PID   Cannot Be Shiny   Games   US & EU & JP 3DS: USUM                                                                Lv. 6    Nature   Hardy   Ability   Static (1)   Item   None   Bundled Item   None   Card Per Save   Only One Allowed    Moves   (ITALIC means Relearnable)   Thunderbolt   Quick Attack   Thunder   Iron Tail   WC ID 1628: 「Ash's Pikachu (Hoenn Cap)」's receiving text 0x2C Thank you for playing Pokémon! Please pick up your gift from the deliveryman in any Pokémon Center.

Wishing Ash's Pikachu (Hoenn Cap) Ash and Pikachu travel across
the ocean to the amazing Hoenn region.
Together with their faithful
companions, they embark on
a high-spirited adventure. Format Ver.1.0.6-3, Post Updated Date:20181110_0044

Species   Vivillon (Fancy Forme)   Nickname   (default, save lang)   OT   GTS   TID   00108   Distribution   Online Wi-Fi   Location   an online Present   Dates   Jul 07 to Jul 31, 2014   PID   Cannot Be Shiny   Games   US & EU 3DS: XY    Lv. 12      Nature   Random   Ability   Shield Dust (1) or Compound Eyes (2)   Item   None 
Souvenir   Moves   (ITALIC means Relearnable)   Gust   Light Screen   Struggle Bug   Hold Hands   WC ID 1503: 「It’s the Fancy Pattern Vivillon!」's receiving text  0x35 Thank you for receiving this distribution! Please pick up your gift from the delivery girl in any Pokémon Center. It’s the Fancy Pattern Vivillon! Here's a Vivillon with the Fancy Pattern,
which you can't normally find, to
commemorate surpassing 100 million
Pokémon traded in the GTS!

Species   Jirachi   Nickname   (default, save lang)   OT   おりひめ   TID   08076   Distribution   Local Wireless   Location   PC Tohoku   Dates   Aug 01 to Aug 31, 2016   PID   Cannot Be Shiny   Games   All Regions 3DS: ORAS                                                                Lv. 100    Nature   Random   Ability   Serene Grace (1)   Item   Star Piece   Card Per Save   Only One Allowed    Moves   (ITALIC means Relearnable)   Wish   Cosmic Power   Swift   Meteor Mash   WC ID 174: 「たなばたまつり2016　ジラーチ」's receiving text 0x51 Thank you for coming to the Pokémon Center Tohoku! Please pick up your gift from the delivery girl in the game.

Classic たなばたまつり2016　ジラーチ 「ポケモンたなばたまつり2016」に
さんか　してくれた　きねんに
ねがいごとポケモン　ジラーチを
プレゼント！
みんなの　ねがいが　とどきますように　ミ☆ Format Ver.1.0.6-2, Post Updated Date:20180411_1627

This Arceus was distributed to SEA players with Pokemon XYORAS.
Only English wonder card, via US and JP units.
Distribution Title Christmas Present - Arceus Wondercard ID 146     PID Cannot Be Shiny Games XYORAS Type Serial Code Dates Dec 21 2015 -
Jan 30 2016 Species Arceus Nickname (default) Gender Genderless Level 100 Nature Random Ability Multitype (1) OT Manesh TID 12215 Location a lovely place Ribbon Classic , Ball Cherish Ball Held Item Silk Scarf Moves Judgment Perish Song Hyper Beam Recover Relearn
Moves (None) (None) (None) (None) Receiving Text 0x2B Thank you for playing Pokémon! Please pick up your gift from the delivery girl in any Pokémon Center.  

Back in December 1999, players are able to obtain a YOSHIRA Mew by trade at Toys R Us stores in the United States, if they were within the first 1500 customers and also caught the Mew on their special "Peel & Win" sticker.

While the DVs are all identical (and not all 15), it can be seen that the Trainer IDs seem to be generated in ascending order.

Huge thanks to @Deoxyz for following up on this and getting it!

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

Check out the save that was dumped, and the full story here:
 

Distribution Title Kanto Classic Gift Wondercard ID 1513     PID Cannot Be Shiny Games ORAS Type Serial Code Dates Mar 15 to
Apr 27, 2016 Species Dragonite Nickname (default) Gender Male Level 62 Nature Random Ability Inner Focus (1) OT Lance TID 3046 Location Pokémon League (Kalos) Ribbon Classic , Ball Cherish Ball Held Item None Moves Agility Slam Barrier Hyper Beam Relearn
Moves Agility Slam Barrier Hyper Beam Receiving Text 0x37 This is a gift from the Pokémon Global Link! Please pick up your gift from the delivery girl in any Pokémon Center. Distribution Text Thank you for participating in the
Kanto Classic Online Competition!
Here is a Dragonite like the one used
by Lance as part of Kanto's Elite Four!  

This event was given away using a common password POYONG for all regions.
While Gardevoirite, Galladite & Lopunnite were given away earlier,
to the participants of the 2017 International Challenge June Competition (Tiny Tourney).
This is the first time that Diancite is obtainable for the games Pokemon Sun & Moon.
 
WC 1620: Mega Stone Gift Gardevoirite
        x 1 0x2C Thank you for playing Pokémon! Please pick up your gift from the deliveryman in any Pokémon Center.
    Galladite   x1   Lopunnite   x1     Diancite   x1                       Serial Code  |  Aug 10 to Oct 31, 2017  |  US & EU 3DS: SM Mega Stone Gift - Gardevoirite
- Galladite
- Lopunnite
- Diancite Format Ver.1.0.5-2, Post Updated Date:20174909_1749

This gift was distributed via Local Wireless to players who went to the 2019 Pokémon World Championships,
held at Washington, DC, in the United States, between August 16 to August 18, 2019.
     Species   Aerodactyl   Nickname   (default, save lang)   OT   Worlds19   TID   081619   Distribution   Local Wireless   Location   a lovely place   Dates   Aug 16 to Aug 18, 2019   PID   Cannot Be Shiny   Games   All Regions 3DS: SM USUM                                                                Lv. 50    Nature   Random   Ability   Unnerve (HA)   Item   Rare Bone   Bundled Item   None   Card Per Save   Only One Allowed    Moves   (ITALIC means Relearnable)   Ancient Power   Rock Polish   Wide Guard   Celebrate   WC ID 685: 「Unearth Aerodactyl’s primeval power!」's receiving text 0x1A Thank you for coming to the 2019 Pokémon World Championships! Please pick up your gift from the deliveryman in any Pokémon Center.

Event Unearth Aerodactyl’s primeval power! Watch out overhead! Leave your
opponents in the dust as you soar
into battle with this terror of the
ancient skies. Format Ver.1.0.8-2, Post Updated Date:20190817_0034

Distribution Title Let's get started! Wondercard ID 590     PID Cannot Be Shiny Games ORAS Type Local Wi-Fi Dates Aug 19 -
21, 2016 Species Bulbasaur Nickname (default) Gender Male Level 5 Nature Random Ability Chlorophyll (HA) OT WORLDS16 TID 8196 Location WCS 2016 Ribbon Event , Ball Cherish Ball Held Item Venusaurite Moves Tackle Growl Celebrate (None) Relearn
Moves Tackle Growl Celebrate (None) Receiving Text 0x19 Thank you for coming to the 2016 Pokémon World Championships! Please pick up your gift from the delivery girl in any Pokémon Center.  

Between 17th June to 14th July 2017, AEON Malls in Japan will be giving away Serial Code,
for various partner Pokemon of Ash's classmates (in the anime).

These Pokemon also received a re-distribution at Pokemon Centers via Local Wireless.
While they look identical to the initial distribution, their wonder card ID is different,
hence allowing repeats.
  Pokemon Physical Serial Code
Collection dates
(Only one allowed) Serial Code End
Redemption Dates
  Pokemon Center
Local Wireless Dates
(Only one type, Once per day) Mallow's Steenee 17 Jun to 25 Jun, 2017 04 Jul, 2017 22 Jul to Aug 13, 2017 Kiawe's Turtonator 26 Jun to 04 Jul, 2017 14 Jul, 2017 22 Jul to Aug 13, 2017 Lillie's Alolan Vulpix "Shiron" 05 Jul to 14 Jul, 2017 24 Jul, 2017 22 Jul to Aug 13, 2017  
 Species   Turtonator   Nickname   (default, save lang)   OT   カキ   TID   170626   Distribution   (Various)   Location   the Pokémon animated show   Dates   (Various)   PID   Cannot Be Shiny   Games   JP 3DS: SM (Serial - 0235)
All Region: SM (Local - 0244)   Lv. 30     Met Lv. 27                                                                  Nature   Brave   Ability   Shell Armor (1)   Item   Moomoo Milk   Bundled Item   None   Card Per Save   (See above) 

Classic   Moves   (ITALIC means Relearnable)   Flamethrower   Shell Trap   Dragon Tail   (None)   WC ID: 「カキのバクガメス　プレゼント」's receiving text 0x2D Thank you for coming to the store! Please pick up your gift from the deliveryman in any Pokémon Center. カキのバクガメス　プレゼント ヴェラかざんのごとく　もえる
あつきこころ！
カキの　バクガメスを　プレゼント！
これからも　アニメでの　かつやくを
たのしみにしていてね！ Format Ver.1.0.5-4, Post Updated Date:20171105_1609

As part of the Let's Go Pikachu promotion worldwide (except Korea), various Cap Pikachu were given away to players via the common code.
The common code for Unova Cap Pikachu is "13LETSGOPIKACHU".
These codes worked for US, EU, JP and TW versions of the 3DS console.
For the JP and TW versions, they can only receive the English version of the wonder card, regardless of language they're playing on.
For the entire duration, players playing Ultra Sun on a US console on FRE language, were given the English card by mistake.
     Species   Unova Cap Pikachu   Nickname   (default, save lang)   OT   Ash   TID   021211   Distribution   Serial Code   Location   a lovely place   Dates   Nov 09 to Dec 01, 2018   PID   Cannot Be Shiny   Games   US & EU & JP 3DS: USUM                                                                Lv. 13    Nature   Hardy   Ability   Static (1)   Item   None   Bundled Item   None   Card Per Save   Only One Allowed    Moves   (ITALIC means Relearnable)   Thunderbolt   Quick Attack   Iron Tail   Volt Tackle   WC ID 1630: 「Ash's Pikachu (Unova Cap)」's receiving text 0x2C Thank you for playing Pokémon! Please pick up your gift from the deliveryman in any Pokémon Center.

Wishing Ash's Pikachu (Unova Cap) When they arrive in Unova, the shadow
of a Legendary Pokémon descends over
Ash and Pikachu. Despite the ominous
introduction, their hearts are filled
with excitement as their
adventure unfolds. Format Ver.1.0.6-3, Post Updated Date:20181110_0111

This event was distributed to players with a 3DS of US, EU or TW regions, via common serial code.
The code was accurately guessed to be PIKACHU20, hours before its reveal on official sites.

The same code can be used to redeem other variations of this Pikachu, provided your save file hasn't received one via wonder card.
The variations receivable follows a schedule.
 
 Species   Pikachu (Kalos Cap)   Nickname   (default, save lang)   OT   Ash   TID   011814   Distribution   Serial Code   Location   a lovely place   Dates   Oct 17 to Oct 23, 2017   PID   Cannot Be Shiny   Games   US & EU & TW 3DS: SM    Lv. 17                                                                  Nature   Hardy   Ability   Static (1)   Item   None   Bundled Item   Pikashunium Z   Card Per Save   Only One Allowed 

Wishing   Moves   (ITALIC means Relearnable)   Thunderbolt   Quick Attack   Iron Tail   Electro Ball   WC ID 627: 「Ash's Pikachu (Kalos Cap)」's receiving text 0x2C Thank you for playing Pokémon! Please pick up your gift from the deliveryman in any Pokémon Center. Ash's Pikachu (Kalos Cap) Ash and Pikachu arrive in Kalos
and discover the mysteries of
Mega Evolution, an Evolution beyond
all Evolution. But Ash's true aim is
to become the Kalos League Champion! Format Ver.1.0.5-4, Post Updated Date:20171018_0141

As part of the Pokemon Halloween Time (ピカピカゴーストパーティ; lit: PikaPika Ghost Party),
it was distributed at Pokemon Centers in Japan, via Local Wireless.
 
 Species   Mimikyu (Disguised)   Nickname   (default, save lang)   OT   ポケセン   TID   170922   Distribution   Local Wireless   Location   a Pokémon Center   Dates   Sep 22 to Nov 16, 2017   PID   Shiny PID   Games   All Regions 3DS: SM    Lv. 10                                                                  Nature   Random   Ability   Disguise (1)   Item   Rare Candy   Bundled Item   None   Card Per Save   Only One Allowed 

Classic   Moves   (ITALIC means Relearnable)   Astonish   Play Rough   Copycat   Substitute   WC ID 248: 「いろちがいの　ミミッキュ　プレゼント」's receiving text 0x08 Thank you for coming to the Pokémon Center! Please pick up your gift from the deliveryman in the game. いろちがいの　ミミッキュ　プレゼント ばける！ピカピカゴーストパーティーの
たのしそうな　ふんいきに　さそわれて
めずらしい　いろちがいの　ミミッキュが
あそびにきたよ！
ともだちに　なってあげてね！ Format Ver.1.0.5-4, Post Updated Date:20171105_1736

This Pokemon was distributed by Serial Code to players in HKTW, at various participating stores.
Tapu Koko is normally not obtainable as a shiny in the game.

As this is a HKTW serial code, this Pokemon can be collected on EU 3DS region (running with English Game Save Language),
and JP 3DS region (regardless of save language).

While redeemable on JP 3DS, this wonder card is only distributed as an ENG wonder card.
 
 Species   Tapu Koko   Nickname   (default, save lang)   OT   Melemele   TID   170428   Distribution   Serial Code   Location   a lovely place   Dates   Apr 28 to Jun 30, 2017   PID   Shiny PID   Games   EU & JP 3DS: SM    Lv. 60                                                                  Nature   Timid    Ability   Electric Surge (1)   Item   Electric Seed   Bundled Item   None 
Classic   Moves   (ITALIC means Relearnable)   Nature's Madness   Discharge   Agility   Electro Ball   WC ID 233: 「Shiny Tapu Koko present !」's receiving text 0x2C Thank you for playing Pokémon! Please pick up your gift from the deliveryman in any Pokémon Center. Shiny Tapu Koko present ! Get this rare shiny Tapu Koko!
Enjoy Pokémon battle together with
the guardian of Melemele Island!!
You can also enter this Pokémon in the WCS 2017.

This event was initially distributed by having players use the Nintendo Zone app at 7SPOTs, in order to grab a serial code,
to commemorate the upcoming release of Movie 20: Pokemon I Choose You in Japan.
The last day to receive a code is August 20th, and the code expiry date is August 28th.
A second distribution was held at Pokemon Centers in Japan via Local Wireless.
Charizard, Piplup or Lucario were distributed together, and only one of three can be received once per day, and players can only receive one of each per game.
 
Distribution Mode Regions Receivable Wonder Card ID Dates Serial Code (only one) JP 3DS Only 0240 Aug 01 to Aug 28, 2017 Local Wireless (only one type;one per day) Any Region 3DS 0245 Aug 22 to Sep 03, 2017  
 Species   Piplup   Nickname   (default, save lang)   OT   マコト   TID   170715   Distribution   (Various)   Location   2017 Pokémon Movie   Dates   (Various)   PID   Cannot Be Shiny   Games   SM; (see above)    Lv. 30     Met Lv. 5                                                                  Nature   Hardy   Ability   Torrent (1)   Item   None   Bundled Item   None   Card Per Save   (See above) 

Wishing   Moves   (ITALIC means Relearnable)   Hydro Pump   Bubble Beam   Whirlpool   Drill Peck   WC: 「キミにきめた！　マコトのポッチャマ」's receiving text 0x2C Thank you for playing Pokémon! Please pick up your gift from the deliveryman in any Pokémon Center. キミにきめた！　マコトのポッチャマ げんきいっぱいで　おとこまさりな
トレーナーの　しょうじょ　マコト
パートナーの　ポケモンは
ポッチャマ　キミにきめた！ Format Ver.1.0.5-4, Post Updated Date:20171105_1639

Distribution Title Wow! It's Zapdos! Wondercard ID 570 PID Shiny Locked PID Games XYORAS Type Serial Code Dates Mar 11 - Sep 30 Nickname (default) Gender Genderless Level 70 Nature Random Ability Hidden Ability OT Aldora TID 3116 Location a lovely place Ribbon Classic , Ball Cherish Ball Held Item None Moves Discharge Thunder Shock Rain Dance Agility Relearn
Moves Discharge Thunder Shock Rain Dance Agility Receiving Text 0x2B Thank you for playing Pokémon! Please pick up your gift from the delivery girl in any Pokémon Center. Distribution Text This Zapdos has a Hidden Ability
for you to discover. You can add it to
your party and let it open the way to
a shocking victory.  

This Diancie was distributed to HKTW players with Pokemon XYORAS.
Only English wonder card, via EU and JP units.
Distribution Title Diancie Gift Wondercard ID 120 PID Shiny Locked PID Games XYORAS Type Serial Code Dates Oct 15 - Nov 30,
2015 Nickname (default) Gender Genderless Level 50 Nature Random Ability Ability 1 OT Universe TID 10045 Location a lovely place Ribbon Classic , Ball Cherish Ball Held Item Normal Gem Moves Diamond Storm Moonblast Reflect Return Relearn
Moves Diamond Storm Moonblast Reflect Return Receiving Text 0x2B Thank you for playing Pokémon! Please pick up your gift from the delivery girl in any Pokémon Center.  

Species   Greninja   Nickname   (default, save lang)   OT   そうせんきょ   TID   00720   Distribution   Local Wireless   Location   Pokémon Movie 16   Dates   Jul 03, 2016 
Jul 16 to Sep 30, 2016   PID   Cannot Be Shiny   Games   All Regions 3DS: XYORAS                                                               Lv. 100    Nature   Random   Ability   Protean (HA)   Item   Master Ball   Card Per Save   Only One Allowed    Moves   (ITALIC means Relearnable)   Hydro Cannon   Gunk Shot   Mat Block   Happy Hour   WC ID 162: 「ゲッコウガ　プレゼント」's receiving text 0x04 Thank you for coming to see the 2016 Pokémon Movie! Please pick up your gift from the delivery girl in any Pokémon Center.

Wishing ゲッコウガ　プレゼント ポケモンえいがを　げきじょうに
みにきてくれて　ありがとう！
「ポケモンそうせんきょ７２０」で
みごと　１いに　えらばれた
ゲッコウガを　プレゼント！
へんげんじざいに　かつやくさせよう！ Format Ver.1.0.6-2, Post Updated Date:20180411_1611

This Pokemon was distributed to players at the 2017 World Championships held at Anaheim, California, via Local Wireless.
This Pokemon being chosen for distribution, is due to it's form being reminiscent of a palm tree:
"Anaheim, California is covered with palm trees, but there is one Pokémon that rises above them all—Alolan Exeggutor"
 
 Species   Exeggutor (Alola)   Nickname   (default, save lang)   OT   Worlds17   TID   081817   Distribution   Local Wireless   Location   WCS 2017   Dates   Aug 18 to Aug 20, 2017   PID   Cannot Be Shiny   Games   All Regions 3DS: SM    Lv. 50                                                                  Nature   Modest    Ability   Harvest (HA)   Item   Sitrus Berry   Bundled Item   None 
Event   Moves   (ITALIC means Relearnable)   Power Swap   Celebrate   Leaf Storm   Draco Meteor   WC ID 617: 「That's no palm tree—it's a Pokémon!」's receiving text 0x18 Thank you for coming to the 2017 Pokémon World Championships! Please pick up your gift from the deliveryman in any Pokémon Center. That's no palm tree—it's a Pokémon! Rise to new heights with your very own
Alolan Exeggutor! Its Harvest Hidden
Ability allows it to reuse its held
Sitrus Berry over and over again during
the sunny weather condition!

When save files are dumped incorrectly or corrupted in some way, they become unusable.
PKHeX will not load save files of incorrect size (and also ignore files with such invalid/missing blocks).
Example of such an error:

Hence, this tool was born. This tool is unable to restore data that was lost! (it can't perform magic, obviously)

There are 2 modes.
Standard Fix and Pokemon Box Salvage.
Always keep backup copies of your saves, even the corrupted ones, before using any tool!
The program will replace the save file that being fixed. (it does keep the original save backup as a .bak file, but know that multiple uses of the software will result in the .bak being replaced)
 
Standard Fix (open spoiler below to read details!)

Pokemon Box Salvage (open spoiler below to read details!)