Dr. Kevin Scanlon This doctor, who was also the physician for the deceased women in the MUFON group, begins treatment of Scully's cancer (Memento Mori). Mulder discovers that Scanlon's "treatments" are, in fact, what killed the women to keep them from learning the true nature of their abductions and their cancer.

Scott Garrett This hitman poses as an investigator and covers up evidence in the investigation of Flight 549's crash. He also attempts to assassinate a witness and ends up killing Agent Danny Pendrell by mistake. After following Mulder aboard another flight, Garrett mysteriously disappears during a mid-air UFO encounter.

Dr. Ernest Calderon An employee of the pharmaceutical company, Prangen Industries, Dr. Calderon conducts a clinical trial experiment in which Emily Sim is a participant (Christmas Carol/Emily). He pretends to treat Emily's physical ailments, but is actually causing her deterioration. He has unknown connections to the government and is ultimately killed by two alien morphers.

Agt. Jeffery Spender Spender is the son of CSM, and shows a definite inclination to follow in his father's footsteps. He weasels his way into running the X-Files with Agt. Fowley, and takes pride in thwarting Mulder and Scully's plans in any way, shape, or form.