- Foiler Footage: An alternate version of the scene where Missy claims her name is an acronym of Mobile Intelligence Systems Interface was shot with her claiming she was a Random Access Neural Interface. The outside scenes of her revealing her identity to the Doctor were shot with Gomez miming that she was the Rani to throw off anyone watching filming. The close up of her saying "Master" was filmed later and other dialogue filled in with ADR.
- I Knew It!: Fans had been theorising for weeks before this episode was broadcast that "Missy" was short for "Mistress".
- Mythology Gag: Missy/The Mistress/The Master has massive Foe Yay with the Doctor, kisses him, and claims to be an android. Sounds familiar.
- Schedule Slip: The death-related content of this episode resulted in an eleventh-hour decision to reclassify this episode in the UK, triggering the necessity of delaying the Series 8 DVD/Blu-ray box set release by a week in order to allow the boxes to be reprinted with the new rating.
- What Could Have Been: According to Michelle Gomez, one take of the sequence where Missy kisses the Doctor originally showed her also holding Clara's hand.
Trivia / Doctor Who S34 E11 "Dark Water"