Serebii Update: Pokémon Sword & Shield Ranked Battle Series 9 ruleset announced. Returns to Series 7 ruleset and no longer permits Restricted Legendary Pokémon. Begins May 1st 2021 https://t.co/gDbXkHSvkT pic.twitter.com/3s46t2Ekmi— Serebii.net (@SerebiiNet) February 15, 2021
Throughout the lifespan of Pokemon Sword & Shield, the competitive scene has had to play by rules almost every month based on official rulesets released by The Pokemon Company International. Following the release of the Crown Tundra DLC back in 2020, the past few months allowed players to use a variety of Legendary and Mythical Pokemon, though a select few of them were still banned. Then, February 2021's ruleset allowed even more Legendary and Mythical Pokemon to be usable.
Now, as of May 2021, the rules will revert back to how they were prior to February. This means that certain Legendary and Mythical Pokemon shall once again be banned, but most Pokemon that can be obtained in The Crown Tundra DLC will still be usable. It is currently unknown how long this ruleset will remain in play once it launches, but if the rules change in the future, then the soonest they shall change will be at the beginning of the following month, June.