I haven't seen anything this scary since I was a kid watching the tv-show Ghostwriter during that Attack of the Slime Monster arc. (I am just now watching this series for the first time, so for me it's been 16 years even though this X-Files episode aired about 2-3 years after Ghostwriter.) That thing messed me up for years and I find dolls creepy to this day. Add that to my fear of possessed children and...well, I won't be sleeping much tonight.
(Note: I do not believe possession of children or dolls is possible, I'm just saying watching it on TV really freaks me out.)