This Pokemon was distributed via serial code by various distributors, to commemorate its appearance the 20th Movie.
Some distributors may require players to pre-order Pokemon Ultra Sun and Ultra Moon.
While US distribution is slated for October 9, and EU distribution is slated for October 1,
Marshadow could be redeemed as early as September 29, if you already have the codes.
Format Ver.1.0.5-3, Post Updated Date:20170929_1459