Start/End Dates	2012-12-07 through 2013-01-10
Country	Japan

Details

The new TV Anime Series Pocket Monsters Best Wishes Season 2 Episode N (ポケットモンスター ベストウイッシュ シーズン2 エピソードN) began airing on January 17th, 2013 and featured the return of the Rocket Gang! To celebrate this, players of the Japanese version of Pocket Monsters Black 2 and White 2 were able to download a Rocket Gang Nyarth. Nyarth has been in the anime series from the very start, more than 15 years, but this is the first time it was offered as a present! Nyarth was be available for a limited time on the Nintendo Wi-Fi Connection from December 7th, 2012 until January 10th, 2013.


Source: http://www.pokemon.co.jp/info/2012/11/121130_g01.html

McDonalds Japan Promotion

As part of a DS at Mac (マックでDS) promotion for Pokémon Mystery Dungeon: Magnagates and the Infinite Labyrinths (ポケモン不思議のダンジョン　～マグナゲートと∞迷宮～), Rocket Gang Nyarth (ロケット団のニャース) was also promoted and distributed at approximately 3,080 out of about 3,300 McDonald's stores across the country as part of their Nintendo Zone service from December 7th, 2012 at 5am until January 10th, 2013 at 19:59 (2012年12月7日（金）5：00～2013年1月10日（木）19：59予定).


Source: http://www.mcd-holdings.co.jp/news/2012/promotion/promo1130.html

Pocket Monsters Best Wishes Season 2 - Episode 21

A preview Pocket Monsters Best Wishes Season 2 Episode N (ポケットモンスターベストウイッシュ シーズン２ エピソードＮ) aired at the end of Pocket Monsters Best Wishes Season 2 - Episode 21. It revealed that episodes from the series would begin airing in January of 2013 and that Rocket Gang would be returning. There was also a quick info brief about this Rocket Gang Nyarth Event download.

Pokémon Smash 114

Later in the week, Shoko-tan also announced the Episode N series, Rocket Gang's return to the anime and the Nyarth distribution event.