The First Doctor is acting like someone with the Values Dissonance of the early 20th century because he's with someone of the early 20th century
This could explain the rather ramped-up and Flanderised sexism and chauvinism of The First Doctor in this episode compared to his prior portrayals, in a way that actually fits with the character - he's trying to keep the Captain on-side and vaguely comfortable by imitating the values an elderly person in 1914 would have. Note how he never makes any "silly" remarks when he's alone with the Twelfth Doctor or Bill (except the bottom-smacking line, but he's arguably in earshot of the Captain for that one). The First Doctor is primarily teasing the Twelfth Doctor.
The only genuinely sexist comment the First Doctor makes is right at the beginning. When the Twelfth Doctor reacts the way he does, the First Doctor then takes it upon himself to yank his current self's chain. Remember that the First Doctor always had a little bit of the Trickster about him, from innocent trolling (e.g. "Chesterfield," "Chesserman," etc.) to malicious (futzing with the Fluid Link in "The Daleks").- Confirmed in the novelisation.
The Twelfth Doctor was thinking of Rose when he regenerated.
Blond hair, young-ish appearance, and female? But also, the music that plays during the Thirteenth Doctor's first few moments is the "Bad Wolf" leitmotif, which first appeared all the way back in Series 1 (In the series premiere, no less!). Maybe the Doctor thought of the companion who first gave him life, all way back when he was a lonely, angry, and bitter man, when he regenerated.- Not a bad theory, but what fans have come to know as "the Bad Wolf leitmotif" was actually composed as the Doctor's leitmotif, originally, hinting at his Dark and Troubled Past with its bittersweetness. And it has been sporadically used as such at other points of the Twelfth Doctor's era, such as in Hell Bent in the execution scene, when the Doctor's heroics in the Time War are referenced. So I'd wager that as far as Murray Gold was concerned, the theme's appearance is only there to reinforce that this is the Doctor and she still has the memories and values of Twelve and all his predecessors.
The Doctor's Name
- The Doctor's name is one of the many variations of Santa Claus, e.g. St. Nicholas, Father Christmas, etc. He tells us in his final speech that his name is something that only children would understand. The Ninth Doctor teased that he was "Father Christmas" after Rose said he was "beamin' away like Father Christmas", to which he replied "Red bicycle when you were twelve." As Eleven he came down a chimney in "A Christmas Carol", and young Kazran promised Abigail that "he comes every Christmas". He also remarked in "Dinosaurs On a Spaceship" that he kept a Christmas list (and Santa keeps a list of who's naughty and nice". As Twelve he knew that the image of Santa wasn't real, and that it was part of a group dream. He also briefly identified as Santa in "The Return of Doctor Mysterio" when Grant offered him a plate of cookies on Christmas Eve. And it fits perfectly with him informing his next regeneration that only children would understand his name.
- It may be, alternatively, that the (somewhat contrary) view that the Doctor's name really is "Who" (suggested in a couple of throwaway gags at various points in the Whoniverse's history) is confirmed here. It's only adults after all who want to complicate matters by suggesting that the title character's name is not as suggested by the title.
The Captain didn't survive long after the 1914 Christmas Truce.
Whilst there may be information on actual historical events to suggest the contrary, it seems only reasonable that (if nothing else) with the war in its early stages, he went on to see further action in which he stood a good chance of being killed, thereby minimising the effects of the time paradox in which he was briefly spared. The Doctor (whom we might presume is secretly well aware of this possibility) dropping him off just in good time for the Truce was just giving him a bit of breathing room as, let's be honest, it's a bit dickish to send a man right back to certain and immediate death.- Of course, even if he did die on the very next day of the fighting, it would still ensure that his family wouldn't have to remember Christmas as the day that he died. "The Doctor, The Widow And The Wardrobe" demonstrates how much that can mean to a parent.
- Averted entirely as some extended universe books published by the company that own the Lethbridge-Stewart Family reveal that the Captain makes it to at least mid 1917.
The TARDIS was trying to get back to the University when the explosion struck.
Specifically, Sexy was trying to bring Twelve to the Vault before his regeneration kicked in. As it was originally built to house the body of Missy, it would have been designed to safely contain an outpouring of regeneration-energy, just in case she managed to cheat death yet again. Unfortunately, Twelve's body was too damaged and he couldn't hold back long enough for the TARDIS to land, although it did make it from 1914 to contemporary times. Hence, the city over which Thirteen is sent plummeting is much more brightly lit than a city from the Captain's era would have been. The Doctor may be destined to never die
The Testimony tries to figure out just why he went on his adventures. That wouldn't be necessary if he ever became part of the Testimomy; they'd have his memories already and would know the answer. Granted, he's a Time Lord, but they have the memories of Nardole, who is also non-human (except for his lungs), so it seems they come for aliens too. The Doctor claims that his memories are so vast that Testimony would shatter to hold them, but they seemingly have the memories of every human who has ever lived or will live (and maybe other species as well), so that may just be a boast.- While the "it would shatter you all" thing was likely just an exaggerated Badass Boast, it's worth bearing in mind that Gallifrey already has its own Brain Upload-based Artificial Afterlife for Time Lords — the Matrix. So it's perfectly plausible that the Testimony might not bother with Time Lords simply because another like-minded project is already preserving their memories, and it would just get messy to have several digital copies of a single Time Lord at opposite ends of the universe.
- Also, while the Testimony are time-travelers, this only seems to be in the past; we never see them reaching past the 52nd century (or whenever it was created… I don't remember). Presumably, the time-travel came in to save up all the people who had died before the Testimony's creation, but from then on they'd handle deaths as they come. Therefore, it could just be that the Doctor is fated to die in a very distant future, distant enough that it hasn't happened yet from the Testimony's linear perspective.
The reason the TARDIS kicked 13 out is because this is the second time the Doctor has destroyed the the TARDIS while regenerating; the first being 10's regeneration into 11.
