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* AscendedFanon:
** 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 that it does.
** There was also a pithy debate about how the War Doctor factored into total of the regenerations. Cleared up and sorted here.
* ActingForTwo: Creator/DanStarkey plays both of the Sontarans featured in the episode. Overlaps with YouLookFamiliar (as he had previously played Strax, Skorr in "[[Recap/DoctorWhoS30E4TheSontaranStratagem The Sontaran Stratagem]]", and Jask in "[[Recap/DoctorWhoS30E17E18TheEndOfTime The End of Time]]") and justified by the fact that they are a clone race, presumably all from the same batch.
* HarpoDoesSomethingFunny: The Twelfth Doctor's first lines were entirely ad-libbed by Creator/PeterCapaldi.
* HeyItsThatPlace: 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 "[[Recap/DoctorWhoS27E1Rose Rose]]" (in particular, the long walking sequence leading up to the "turn of the Earth" speech).
* LateExportForYou: Viewers who get their Doctor Who off BBC Entertainment Asia had to wait until February 2015 for the special to air in their region. It would have been NoExportForYou, but after getting angry letters from Whovians from all over Asia throughout December 2013 and all through 2014, Creator/TheBBC finally relented.
* MilestoneCelebration: 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.
* OnSetInjury: The cane the Doctor uses was actually necessitated by Creator/MattSmith injuring himself on set.
* TheOtherDarrin: Clara's father is played by James Buller in this episode, while previously in "[[Recap/DoctorWhoS33E7TheRingsOfAkhaten The Rings of Akhaten]]" he was played by Michael Dixon. Of course, it works here because Clara's dad is 8 years older.
* RealLifeWritesTheHairstyle: Creator/MattSmith and Creator/KarenGillan both had to wear wigs for this episode as they'd both shaved their heads for other roles (Smith for ''Film/LostRiver'' and Gillan for ''Film/GuardiansOfTheGalaxy2014''). Karen later agreed they missed an opportunity to get a picture of themselves wearing each other's wigs.
* RecastAsARegular: Creator/PeterCapaldi had previously played [[Recap/DoctorWhoS30E2TheFiresOfPompeii Caecilius]] and [[Series/TorchwoodChildrenOfEarth John Frobisher]].
* ThrowItIn:
** Creator/MattSmith shaved his head for a role in the film ''Film/LostRiver'', 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.
** Creator/PeterCapaldi's first lines as the Doctor were improvised. Creator/JennaColeman described his outburst of "Kidneys!" as singing.
* WhatCouldHaveBeen:
** Creator/StevenMoffat originally had plans for an entire Series 8 with the Eleventh Doctor set on Trenzalore, but Creator/MattSmith's decision to step back after the end of Series 7 threw a kink in that plan. The plot of "Time" is essentially most of Moffat's ideas for that Series 8 storyline condensed into an hour long episode.
** During his regeneration, Moffat thought of having cameos from many of the Eleventh Doctor's friends to say farewell. With discussion and scaling back, it was decided that only Amy Pond would appear.
* WorkingTitle: ''The Twelfth Night''.
* WrittenInInfirmity: The Doctor start walking with a cane and a limp midway through the episode; in real life, this is due to an injury Creator/MattSmith suffered. The reason the Doctor walks with a cane is because he loses 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''.)
* YouLookFamiliar:
** Look:
*** Sheila Reid (Gran) had played [[Recap/DoctorWhoS22E2VengeanceOnVaros 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.
** Sound:
*** Elizabeth Rider (Linda) voiced the ATMOS system in [[Recap/DoctorWhoS30E4TheSontaranStratagem "The Sontaran Stratagem"]]/[[Recap/DoctorWhoS30E5ThePoisonSky "The Poison Sky"]] two-parter. She also played Mistress Ellen in ''Recap/TheSarahJaneAdventures'' episode [[Recap/TheSarahJaneAdventuresS4E9E10LostInTime "Lost in Time"]] as well.
*** In post-production, the voices emanating through the crack in time from Gallifrey were provided by Ken Bones, who had been the Time Lord General in "[[Recap/DoctorWho50thASTheDayOfTheDoctor The Day of the Doctor]]".

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