Without (2) - S8-E2
Corrected entry: In an earlier season, X said that a device for piercing the back of the neck was needed to kill the alien bounty hunter, because a gun shot "wouldn't do." However, Scully is able to kill the bounty hunter with a gunshot to the back of the neck. (00:37:20)
Correction: X probably meant that a gunshot to the body, not a gunshot to the neck, wouldn't work.