Pokemon World Championships were rocked by a "perfect storm" of trading glitches and anti-cheat rules, all because of Pokemon Legends Arceus

gamesradar.com:

A number of competitive Pokemon players have spoken out in response to last-minute changes that saw them disqualified from this year's World Championships.

Back in August, the Pokemon World Championships were held in Yokohama, Japan. As the tournament progressed through its first day, however, several players revealed that they had been pulled out of their games and disqualified from the tournament. It sparked a substantial debate in the community at the time, and now several of the players who fell foul of the new rules have explained exactly what happened, largely in a new video with YouTuber Pokemon Challenges.

In the weeks leading up to the tournament, The Pokemon Company made two substantial changes to the game's competitive scene. The first was a change in ruleset, with the arrival of Pokemon Home opening the floodgates for dozens of new Pokemon - several of them competitively viable - to enter the competitive scene. With a shift in the meta that sizeable, players would have limited time to craft their new teams ahead of the competition.

The second was a tweak to the hack checks that have been part of competitive Pokemon for some time. The Pokemon Company warned players that it had changed the tools it used to determine a Pokemon's legitimacy ahead of the event, stating that "we strongly recommend you do not use Pokemon provided to you by other people as some indicators that a Pokemon was illegally modified are hidden."

The issue in this tournament appears to hinge on Pokemon Home and a community tool, PKHex, which players can use to generate tournament-viable Pokemon. In Pokemon Challenges' video, competitive player Brady Smith, who was disqualified from the tournament after winning their first two games, claims