Michelle Veintimilla returns to reprise the role of Bridgit Pike/Firefly, following an extended absence where the character was portrayed by Camila Perez.
On the doorway before the headmaster's office, there's an inscribed motto: "Eruditio populi liberi spes gentium." That's Latin for "The education of free people is the hope of humanity."
Ecco may also be based on or a reference to Alicia Hunt from Batman (1989), who was a blonde mistress and accomplice to Jack Napier/The Joker and later wore a porcelain mask due to a disfigurement upon her face, much like Ecco's Mummer mask. The porcelain mask worn by Alicia Hunt and Ecco is based on a mask worn by the disfigured character Christiane from Eyes Without a Face (1960).
Francesca Root-Dodson said that she got to keep Ecco's outfit this episode when the filming of the series wrapped up.
Ecco's name may possibly be a homage to the character of Isabelle Cheranova aka Echo, who was a Russian assassin that fought Batman during the events of the No Man's Land comic crossover event, an event that served as partial basis for the last episode of Season 4 as well as the entirety of Season 5.