Solbor was only intended as a minor character to begin with. But the producers were so impressed with James Otis, and what he brought to the Pah-wraith sequence that his role was expanded.
This episode was originally titled "Umbra", which is an area of deep shadow. This was to follow on from the previous episode, Penumbra (1999), an area of half-shadow.
Worf's claim that no one who has ever seen what is underneath a Breen's helmet has lived to tell of it seems to contradict the episode Indiscretion (1995), where Kira and Dukat knock out two Breen guards and take their uniforms, including the helmets.
Dukat's reference to a single ship fighting against the entire Klingon Empire refers to his acquisition of a Bird-of-Prey in Return to Grace (1996), which he used to make hit-and-run attacks on the Klingons in Cardassian space until By Inferno's Light (1997).
This episode is the only time that Sarah refers to Sisko as her son.