A special stage featuring Pinsir is available to play once per day between May 7th, 2015 at 06:00 UTC and May 11th, 2015 at 06:00 UTC. Players that catch Pinsir are able to use it as their own Pokémon and take advantage of its Power of 4 skill. When players use this skill, their attack does more damage when they make a match of four.
Details of this event have been added to our Pokémon Shuffle Special Event page.
Sources:
http://www.pokemonshuffle.com/en-us/connectivity#pinsir-launch and
http://www.pokemon.co.jp/ex/poketoru/news/post.php/36/