A Shiny Gengar was announced to be distributed in Japan. Distribution will be done via serial code which you can receive at 7-11 7-Spot.
Like the Shiny Gardevoir it's based on a character from the movie.
Pokemon: Shiny Gengar
Gender:
Level: 50
OT: ジャービス
ID: 07096
Ability: Levitate
Nature: Random
Moves:
Mean Look
Hypnosis
Psychic
Hyper Beam
Item: Gengarite
Pokeball: Cherish Ball
Ribbon: Whishing Ribbon
Location: Pokemon Movie 16
Dates: July 9 - 15, redemmable until August 31, 2016 / July 30 - August 31, 2016
Game Distribution: XY, ORAS
Distribution Type: Serialcode / Local Wireless
Distribution Location: 7-11, 7-Spot / Pokemon Centers, Pokemon Stores
Sources: http://www.pokemon.co.jp/info/2016/07/160701_cm02.html / http://www.pokemon.co.jp/info/2016/07/160701_cm02.html