Previously it was revealed that the 17th movie will also feature Yveltal, Xerneas, and 12 of the Mega Evolutions. This movie will be coming out in theaters on July 19.
Description from scan
A Pokémon that gives birth to diamonds - that is Diancie! Diancie is Rock/Fairy-type! In battle, it can create many diamonds from both hands, and use them to protect itself. A reliable battle partner!!