Season two, episode four, "Photo Finish". As a child, Robert Englund, who was anxious to watch a Western, wound up watching The Bad Seed (1956) due to a mix-up at the television station. He's been quoted as saying, "For years I was frightened of girls with pigtails." In this episode, he got to face-off with the now grown-up girl that terrified him, Patty McCormack.
This is also known as "FreddySomething", which is a take on the television series, Thirtysomething (1987).
Season one, episode two, "It's a Miserable Life", in the hospital, there's a poster in view that reads "Mom and Dad, I use drugs!" This is the first time this poster was seen in the series, but it became a regular staple of the set dressing in subsequent episodes.
There are several Star Trek references: The psychologist is named Dr. Picard, like Captain Picard from Star Trek: The Next Generation (1987). When Johnny disintegrates, his last words are "Beam me up, Scotty". During Dr. Picard's daydream, when he's infected, he shouts "Captain, the dilithium crystals are gone!". Tim Russ, who played Dr. Picard, went on to star in Star Trek: Voyager (1995) as Commander Tuvok.
The house, in which John lives, is the same house, in which the Blocker family lived, earlier in the season.
Season two, episode seventeen, "Interior Loft Later", is the only sequel episode that was filmed and aired consecutively with the episode it followed.