- 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.
- At a Royal Television Society event, Steven Moffat revealed a decoy version of Missy's reveal in the episode was shot in case any members of the public overheard: You know who I am. I'm Missy. Or, if you'd prefer, Random Access Neural Integrator. Rani for short.
Trivia / Doctor Who S34 E11 "Dark Water"