In September 2016, Firaxis games released XCOM 2, a turn based strategy game where the player defends the world from an alien invasion. War of the Chosen is the biggest expansion to date, announced at E3 2017.
War of the Chosen will add 3 champions of the invading enemies who you fight throughout the game. You will fight each chosen several times throughout the game, and each time they will get stronger and gain new abilities. They progress like the player does, so each fight is unique. Each of the three chosen have their own fighting styles for even more variety in their fights. See the announce trailer below.
The expansion will be released on August 29th, 2017.