A Kobold is kind a goblin or evil spirit in German folklore.
Actor James Remar says The X-Files saved his life. He had been in New York City that summer, riding the Ladder Company 3 truck with friend Patrick Brown. The show induced him to take the role, and he joined the cast and crew days before 9/11 happened. Ladder Company 3 suffered some of the heaviest casualties that day, including Brown.
This is the first time that Satan is overtly suggested as the antagonist. This is also the first time that Doggett and Reyes confront a demonic entity in an X-File; Scully has been in four satanic X-Files in the past, Die Hand Die Verletzt (1995), All Souls (1998), Terms of Endearment (1999), and Orison (2000).
The theme of demonic possession freaked out Robert Patrick, so much so that the usually highly professional actor had difficulty remembering his lines.
With this episode, Scully is officially off the X-Files and is now a lecturer at the FBI Academy at Quantico. The scenes for this were shot at a lecture hall at UCLA.