One scene that always had a "creepy factor" for me was from The Lights of Zetar
, when that poor woman on the floor on Memory Alpha lifts her head and begins the speak in (I assume) the language of the Zetarians. That posterized (or whatever they call that) effect on her face, combined with the croaking sounds she makes, and lowering her dying head to the floor, frozen in a twisted expression, was always unsettling to me.
(Not Next Generation
, I know, but it sprang to mind readily when I read these accounts!)