Alice Krige, the voice of the Borg Queen, played the role in Star Trek: First Contact (1996) and the series finale of Star Trek: Voyager (1995).
Most of the training scenarios are based on events that occurred in previous Star Trek episodes and films.
Alice Krige recorded her dialogue for this episode in her husband's closet during the Covid-19 lockdown.
Shari Yen Yem (the test monitor) is a Pandronian colony life-form of the same species as Ari Ben Bem from Bem (1974). Bem was also tasked with testing Starfleet personnel, but in a somewhat more perilous, real life situation.
The scene in which mirror Boimler points and shrieks at Mariner is parodying Invasion of the Body Snatchers (1978), people replaced by the alien seed pods would point and shriek to identify humans hiding among them. This movie also starred Star Trek actor Leonard Nimoy.