Marshadow has been officially confirmed for Sun and Moon. There are currently no details on when and how the promotion will take place, but The Pokemon Company said it’s coming “soon”.
Marshadow is a mythical GHOST FIGHTING Pokemon. This promotion is tied with the upcoming “I Choose You” movie where it appears with Ash.
Marshadow was found in the ROM dumps months ago, but was not available up to this point. There is no details on the distribution mechanism.
Here is what Bulbapedia shared about Marshadow:
Marshadow is a bipedal Pokémon that is usually gray. The area around its face resembles that of certain headgear such as a wrestler’s mask or a helmet. The headgear can turn green when attacking or using its exclusive Z-Move. The bulbs on its arms can also turn green. It has orange eyes with golden yellow pupils. The spots above its eyes are the same color as its pupils. Marshadow has two trails of shadows coming out from behind its legs.
Very few people have seen it, so its existence was the stuff of legends and myths.