https://www.polygon.com/2017/8/28/16216902/pokemon-sun-and-moon-marshadow-gamestop-giveaway

The first chance to get Marshadow, one of the newest legendary Pokémon, is coming this October. GameStop will have codes to unlock Marshadow in Pokémon Sun and Pokémon Moon, and it will come with a special Z-Crystal item to boot.

Marshadow’s release will come just weeks before Pokémon Ultra Sun and Ultra Moon, the continuations of last year’s mainline Pokémon entries. The Pokémon Company has teased the series’ only ghost- and fighting-type for several months, however, revealing it in full this spring. Dataminers first uncovered Marshadow a few weeks after Sun and Moon launched last fall.