- Ascended Fanon:
- Yes, we can finally confirm that mirrors freeze Weeping Angels!
- Many fans have speculated and argued over whether the Tenth Doctor's aborted regeneration actually counted towards the total. Now we know.
- There was also a pithy debate about how the War Doctor factored into total of the regenerations. Cleared up and sorted here.
- Acting for Two: Dan Starkey plays both of the Sontarans featured in the episode. Overlaps with You Look Familiar (as he had previously played Strax, Skorr in "The Sontaran Stratagem", and Jask in "The End of Time") and justified by the fact that they are a clone race, presumably all from the same batch.
- Harpo Does Something Funny: The Twelfth Doctor's first lines were entirely ad-libbed by Peter Capaldi.
- Hey, It's That Place!: The block of flats where Clara's family are having Christmas dinner is the same one used in some shots of the Powell Estate in "Rose" (in particular, the long walking sequence leading up to the "turn of the Earth" speech).
- History Repeats: Matt was recovering from a nasty leg injury while filming the final episode of his tenure. David Tennant also filmed his final episode while recovering from an injury, his being an ailing back that he'd recently had worked on with surgery.
- Milestone Celebration: Though the episode is primarily a Christmas special, it also happens to be the 800th episode of Doctor Who, and a big one at that the Eleventh Doctor regenerates and the Twelfth Doctor takes over from here as the first of a new regenerative cycle. On top of all that, it also closed the franchise's 50th anniversary year.
- The Other Darrin: Clara's father is played by James Buller in this episode, while previously in "The Rings of Akhaten" he was played by Michael Dixon. Of course, it works here because Clara's dad is 8 years older.
- Recast as a Regular: Peter Capaldi had previously played Caecilius and John Frobisher.
- Throw It In!:
- Matt Smith shaved his head for a role in the film Lost River, and it did not grow back in time to reform his Doctor's signature coif for his final episode. He shaved his head again for a bald cap and donned a wig. A script re-write incorporated the wig into the story, leading to several of the episode's funniest moments.
- Peter Capaldi's first lines as the Doctor were improvised. Jenna Coleman described his outburst of "Kidneys!" as singing.
- What Could Have Been:
- Steven Moffat originally had plans for an entire Series 8 with the Eleventh Doctor set on Trenzalore, but Matt Smith's decision to step back after the end of Series 7 threw a kink in that plan. The story is essentially most of Moffat's ideas for that Series 8 condensed into an hour long episode.
- During the regeneration scene, Moffat initially hoped to include cameo appearances by many of the Eleventh Doctor's friends. Apart from Clara, these included Amy Pond, Rory Williams, River Song, Brian Williams, Madame Vastra, Jenny Flint, Commander Strax, Dorium Maldovar, plus Craig Owens, his wife Sophie and their son Alfie (aka Stormageddon). Later, these plans were scaled back, eliminating some characters but adding Barnable and Handles, before it was finally decided that only Amy would appear.
- Working Title: The Twelfth Night.
- Written-In Infirmity: The Doctor start walking with a cane and a limp midway through the episode; in real life, this is due to an injury Matt Smith suffered. As SF Debris joked, Moffat was lucky Smith hadn't lost a limb or two by this point. Ironically, the reason the Doctor walks with a cane is because he actually does lose a leg during his time on Trenzalore, but references to this were cut from the final script (though maintained in the spin-off short story collection, Tales of Trenzalore.)
- You Look Familiar:
- Sheila Reid (Gran) had played Etta.
- Dan Starkey (Strax) as a pair of different Sontarans. Although Starkey has been playing different Sontarans on screen dating back to 2008, this is the first episode since the introduction of Strax in which he has appeared as different Sontarans.
- You Sound Familiar:
Trivia / Doctor Who 2013 CS "The Time of the Doctor"