The Crown Tundra, the next DLC for Pokémon Sword and Shield releasing as part of the game's Expansion Pass, will bring an enormous new map and more than 100 additional Pokémon. It will also add a powerful new item to the game: the Ability Patch.
The Pokémon Company hasn't revealed yet how an Ability Patch can be acquired, only saying that it will be tricky. Still, it's definitely worth the effort because it will let you change your Pokémon's ability to that species' Hidden Ability. Most Pokémon species have the potential to learn one of the game's 153 Hidden Abilities, but there's no way to check ahead of time within the game. Considering how valuable the Ability Patch is likely to be, and that there's no clear way to change the ability back, you should consult Bulbapedia before using the item.
Previously, the only way to acquire a Pokémon with a Hidden Ability was to defeat it in a Max Raid Battle or to breed it at the Pokémon Nursery, so the Ability Patch gives you a lot more control over the process.
When combined with Max Soup from the Isle of Armor expansion, an Ability Patch can also be used to reveal the Hidden Ability of your initial partner Pokémon and allow it to Gigantamax. The starters have had access to Gigantamax evolutions since the release of Isle of Armor, so if you've already powered them up you can just save your Max Soup for one of the other Pokémon capable of Gigantamaxing.
The Crown Tundra releases on Oct. 22 so check back here for more information on how to take advantage of all the new features in the DLC including how to actually get an Ability Patch.