Scully bases the notion of Barry's mental illness on reports of Phineas Gage, who supposedly underwent a personality change after a blasting accident drove an iron rod through his head and out the other side. However, the idea that Gage became violent, immoral, or a pathological liar, like Scully describes him, is an urban legend. Gage lived a productive life for 12 years following his accident.
When the power goes out Mulder calls Barry from his cell phone as they have lost the "captured line". Then Barry is seen talking to Mulder on a cordless phone. Cordless phones will not work without power.
Real snipers or SWAT teams do not have rifles that point laser beams so that the person targeted (in this case Duane Barry) can see the laser beam.
Standard red lasers can not be seen by the naked eye; special effects fabrications just use a small, red LED bulb, a simple pocket laser and blow fine smoke or powder past the lens to make them visible on film; usually the least expensive effect in film and video. It's the set up *around* the laser effects that can cost the production company.
The ear implant that Mulder wears when he enters the hostage situation did not exist at the time of filming. Something like it does today.
During the opening alien visitation you can see the top left alien tilt his head to the left, revealing a human skin tone and collar of a body suit.