The official Japanese YouTube Channel posted a video for the Pikachu Mega Campaign (ピカチュウの メガキャンペーン) which will take place at the Pokémon Centers starting on December 12th, 2015. This is part one of the campaign and another part will be announced at a later date. Images from the video have been added to an Imageboard thread.
Patrons that spend at least 2,000 yen on merchandise at the store can receive 1 of 8 different Poncho Pikachu cards with an accompanying Clear File. The presents feature: Pikachu with Mega Rayquaza poncho, Pikachu with Mega Tabunne Poncho, Pikachu with Mega Tyltalis poncho, Pikachu with Mega Yadoran poncho, Pikachu with Mega Lizardon X poncho, Pikachu with Mega Lizardon Y poncho and Pikachu with Mega Lucario poncho.
An alternate-colored Diancie will be distributed from December 12th, 2015 until December 31st, 2015 to players of Omega Ruby or Alpha Sapphire. Details were not revealed.
Players of Pokémon Tretta Ultimate Z can also receive a Mega Lizardon X or Mega Gyarados trophy tretta.