A competitive stage featuring Mega Banette is available for play and players can attempt it as many times as they want each day. The competitive stage will be available from
April 30th, 2015 until May 7th, 2015. Players are ranked based on their high score and the overall results of this competitive stage will be announced on May 7th, 2015 at 06:00 UTC. The top 10,000 players in Europe, the top 20,000 players in North America and top 50,000 players in Japan can earn a Banettite. Banette can be caught in stage 177.
Details of this event have been added to our Pokémon Shuffle event page.
Source:
http://www.pokemonshuffle.com/en-us/connectivity#banette-launch