This West African immigrant lacks a pituitary gland, and must hunt down other humans to steal what he lacks. In West African folklore, Aboah's kind are known as The Teliko. On the verge of finishing off Mulder, Aboah is shot by Scully.
This internet stalker likes to suck the fat from his dates. He secretes a digestive substance which renders the victim's fat, which he ingests before the body dissolves entirely. He is apprehended and is currently in prison, with a really bad case of dry skin.
Eddie is responsible for impregnating several women. He has inherited an anomalous muscular structure beneath his skin that allows him to take on any form that he chooses. Once he is incarcerated, he is dosed with muscle relaxants to keep him from shape-shifting.
Years ago, Mulder was responsible for sending Barnett to prison, where he supposedly died. But in reality, he became a guinea pig in age-reversal experiments conducted by Dr. Joe Ridley. After John loses a hand, Dr. Ridley is able to regenerate Barnett's lost appendage using a salamandar.
These forest creatures begin attacking humans in response to encroaching development. They can blend perfectly with their surroundings, and are highly intelligent. Mulder speculates that they could be members of Ponce De Leon's expedition to find the Fountain of Youth. He theorizes that perhaps they found the secret to longevity, and over time evolved into these creatures.
