Movie20: Marshadow .

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.
 

Species   Marshadow   Nickname   (default, save lang)   OT   M. del Passo   TID   100917   Distribution   Serial Code   Location   a lovely place   Dates   Oct 01 to Oct 23, 2017   PID   Cannot Be Shiny   Games   EU 3DS: SM

Lv. 50

Nature   Random   Ability   Technician (1)   Item   None   Bundled Item   Marshadium Z  Classic

Moves   (ITALIC means Relearnable)   Spectral Thief   Close Combat   Force Palm   Shadow Ball

WC ID 626: 「L'enigmatico Marshadow!」's receiving text

0x2C Thank you for playing Pokémon! Please pick up your gift from the deliveryman in any Pokémon Center.

Format Ver.1.0.5-3, Post Updated Date:20170929_1502