The official POKKÉN TOURNAMENT website announced that Jukain (ジュカイン) is the new playable Pokémon that will be added to the arcade game in Japan on December 16th, 2015. A video was posted on Namco's YouTube Channel. Farfetch'd and Electrode were also announced as new Support Pokémon.
Jukain Video
Shoko-tan Picture
A picture of Shoko-tan playing the game was posted on Monday December 7th, 2015 that accidentally showed the move list for Jukain, revealing the new playable Pokémon before the official announcement.