First speaking appearance of classic Ducktales villainess Magica DeSpell. Here she appears in shadow form and has a British Accent rather then a Romanian Accent.
Posters for Glomgold products are on the walls of the abandoned subway car.
The Terra-Firmians were originally created for the Uncle Scrooge comics by Carl Barks. They were divided into two factions: the Terrians and the Firmians. When they appeared on the original DuckTales (1987) animated series, however, they were merged into one group.
The colours of the Terrifermians encountered are the exact same colours as Huey, Dewey, Louie, Webby and Lena.
Huey questions why anyone would attack someone in the shower. This is obviously a reference to Alfred Hitchcock's Psycho (1960) which features a famous scene of a woman being killed in the shower.