The Lost are a new type of enemy introduced in XCOM 2: War of the Chosen.
The Lost (or Drak-ten, in the ADVENT language) used to be human, but exposure to the alien bio-weapons used in the initial invasion has caused them to devolve into bloodthirsty zombie-like monsters. They dwell in the abandoned cities, and despite ADVENT's best efforts they continue to thwart colonization attempts.
Individually, Lost are frail (4 HP at most) and restricted to melee attacks. However, the Lost are never found alone- they respawn infinitely on the maps that they appear, allowing them to overwhelm even hardened soldiers through sheer numbers. Lost swarms are attracted to loud noises, and using explosives will cause then to spawn faster.
To compensate for their swarm tactics, a special mechanic called Headshots applies when fighting Lost. Any standard shot that kills a Lost is a free action, allowing a soldier to kill as many Lost as he has rounds available so long as he doesn't miss. They are also especially weak to fire; Burning does bonus damage to them and they cannot attack while burning. As a result, it is advised to take a flamethrower on any mission featuring the Lost. A Bladestorm Ranger can also be effective so long as the Ranger doesn't miss.
Despite being biological, they are feral and so cannot be mind-controlled or affected by abilities requiring Will tests.
It should be noted that the Lost will attack ADVENT and aliens just as readily as they will attack XCOM; in conjunction with the Ultrasonic Lure item gained from their autopsy, they can be used to distract more dangerous enemies (especially in conjunction with explosions to get their attention).
In addition to the standard Lost, two variations appear that can be spawned within Lost swarms:
- Lost Dasher: These Lost are especially swift, requiring a full dash move to escape from them.
- Lost Brute: These Lost inflict more damage and have high health, potentially ending a Headshot chain. However, they are sluggish compared to the other types of Lost.