Multiple sources are showing a 2016 release for the crowdfunded successor.
http://www.nintendoworldreport.com/rumor/40801/mighty-no-9-possibly-delayed-at-retail
Multiple retail outlets are now showing the physical version of Mighty No 9 with a 2016 release date.
The following websites have updated their release dates for Mighty No 9 to "December 31, 2016": Amazon (both US and Canada), GameStop, EB Games, GameFly, Walmart (US/Canada), Best Buy (Canada). As of press time, Best Buy's US site and Target still show the game with the previous September 15 release date.
Deep Silver has not commented on the change when approached by Videogamer, while the backer forums have said "The release date is the same". As well, the game's Steam listing still lists September 15, so it may be the physical copies that are held up.
