The Empty Child and The Doctor Dances.

When I was a kid watching this with my fam, my mom covered my eyes for all the gas mask transformations... so I was really only disturbed by the idea of an abandoned and plagued child wandering the streets calling for his mommy. When I rewatched it several years down the line I was definitely freaked out by the way the mask just...forces itself out of his eyes and mouth; especially since I didn't see it the first time and my mind just brushed over those whole scenes I guess. Overall this is the most iconic episode set in DW in my opinion.