https://www.gamespot.com/articles/free-mythical-pokemon-zeraora-will-be-available-so/1100-6462168/

Pokemon fans will soon have a chance to get their hands on October's free Legendary Pokemon for Ultra Sun and Ultra Moon, but those aren't the only rare monsters up for grabs this month. To commemorate the release of the upcoming Lost Thunder expansion for Pokemon TCG, The Pokemon Company is also giving away a rare Mythical Pokemon for the 3DS games this month: the Thunderclap Pokemon Zeraora.

First revealed this past April, Zeraora is a fast, cat-like Electric-type monster debuting in the latest Pokemon movie, The Power of Us. This marks the first opportunity players will have to get their hands on one; like other Mythical Pokemon, Zeraora isn't obtainable within the actual games, so you'll want to add one to your collection while you can.