World Championships Stamped Cards
1. World Championship 2012 Zorua 025/BW
The source of this card is often misleadingly/abstractly described as ‘WC2012 Participation Promo’, or sometimes more narrowly as ‘WC2012 Trials Promo’ but this card is actually tied to an event called 빙고랠리 Bingo Rally, that took place during the WC2012 Trials, which did not require you to participate in the actual tournament. If you wanted to participate, you had to collect stickers from a variety of events that took place on-site.
The top right of the Bingo card reads: Even for just participating, you can obtain a Zorua promo card!
As can be seen from the flyer: Zorua was awarded for participating, and the badge was for completing two bingo rows. Everyone can participate. I did not find whether participating meant obtaining at least one sticker, or by simply signing up for the event.
2. World Championship 2013 Team Plasma Ball
This card does, for some reason, not appear on the PTCG website.
There is very little info about how this card could be obtained, but multiple sources cite WCS2013 Trials Participation, which is indeed correct this time (unlike the Zorua above) and only players who register as TCG players received it (I believe VGC players did not obtain it).
From a variety of posters that can be seen in blog posts covering the event back in 2012, Team Plasma was key to some of the themes/events on-site. It was also, obviously, key to the card sets and games released during the time.
After hours of digging, I managed to find the below photo confirming that the distribution of this card was indeed tied to registering as a player in the tournament.
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Translation: (This is) the certificate and promo card received after registering as a player!
Honestly, that card… comes out a lot in BW8 (crying).
This was a common card to play during the era, and also a card that in itself was not of high rarity. The promo, however, is very rare and copies are difficult to find. This is pop 3 (all three BRG 9, with none graded higher).
3. WCS 2014 Promo - Team Flare Rookie
Awarded to Participants in the 1st and 2nd round of the Trials.
4. World Championship 2015 M Absol EX, Absol EX
The two promos were also awarded for participations (registration) in the Trials. Absol EX was given to 1st and 2nd round participants. M Absol EX was given to 3rd and Final round participants.
(I left in the original comment where the OP notes, that the card is absolutely useless and, hence, they don’t want it - this shows the state of collecting at the time quite well!)
5. World Championship 2016 M Garchomp EX, Garchomp EX and Garchomp Spirit Link
The M Garchomp, probably the most common WCS-stamped Korean promo, was awarded on-site to everyone who added Pokemon Korea as a friend (or followed, rather) on Kakao (Korea’s messaging and chatting app). The other two cards were awarded for reaching 100 points in the TCG tournament section.
6. World Championship 2018 Energies
[in progress - couldn’t find much info on distribution]
There were no more WCS (National) events after 2018.
In 2019, Pokemon Korea introduced the Korean League system, where players accumulate points throughout the season, rather than compete
in open-to-all tournament at the end of the year (as was the case with the WCS).