https://www.gamespot.com/articles/another-free-mythical-pokemon-is-now-available-for/1100-6453899/

The latest Pokemon giveaway from Sun and Moon has now begun. For a limited time, players have a chance to add the Mythical Pokemon Marshadow to their teams, making this the first time the rare Fighting/Ghost-type Pokemon has been available in the games.

To claim your Marshadow, US players will have to pick up a free download code from a GameStop store; those in the UK, meanwhile, will have to visiting "participating retailers" for their free code. Marshadow comes at level 50 and is equipped with Marshadium Z, which allows it to use the exclusive Z-Move Soul-Stealing 7-Star Strike once per battle. It also knows the following attacks: