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 sown their eyes, mouth and nose in order to prevent themselves being infected by Purity and as such are 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 blood is non-toxic to humans).

Unlike many X-Files villains the Faceless Aliens are trying to accomplish a necessary evil by purging the Galaxy of those who could be exposed to the Purity virus but do so in a very extreme manner that holds no value for life - though the Faceless Aliens may well argue their deeds are of the "killing thousands to save billions" school of thinking.