In a video published on XCOM's YouTube Channel, senior producer Garth DeAngeles walks through some of the game's next expansion, XCOM 2: War of the Chosen.
The expansion's premise is reclaiming areas of earth still ravaged by the first invasion, so it sounds like it'll either touch on the aftermath of some parts of the first game, or it'll be picking up from the main plot of the second. The player's goal is to get two factions to work together to defeat what are called the Lost and Abandoned, the enemy types populating the expansion. Those two factions are the Reapers, comprised of sharpshooters; the Skirmishers, who seem tank-like, with melee and ranged capability; there is another faction included in a short cutscene called the Templars, but they aren't featured beyond that.
The two missions featured are escort quests, where the players must take the leader of one faction to a rendezvous with another. The Lost attack in packs, and, in another zombie trait, are drawn to explosions.
The major antagonist featured is called the Assassin, who tries to stun the player's troops before scurrying away with them. The strategy emphasized with the Assassin is knocking her defenses to a minimum.
The Lost don't take cover, and only attack with melee. Headshots and strategic placement above the enemy are encouraged.
Find out more on the XCOM 2 blog
XCOM 2: War of the Chosen releases August 28th, 2017
