Faceless aliens
The Faceless Aliens are a faction of alien beings in the X-Files who oppose the colonization of Earth by the Colonists as well as the spread of Purity - they are named after the fact that they have no visible facial features and are said to be one of the few species in the galaxy not infected by Purity (the other being humanity).

The Faceless Aliens are infamous for their miniature flame-throwers, which they utilize with deadly proficiency and attack their victims en mass - they target abductees and usually burn them alive (often in large numbers).

The Faceless Aliens are connected to the Alien Bounty-Hunters and are considered to be offshots of the same species - they even bleed the same green ooze (however unlike Bounty-Hunters the Faceless Aliens bloos is non-toxic to humans).