This is an extremely spoilerific reveal about the Series 10 finale – specifically, Episode 12. Firstly, not only do we know that Michelle Gomez’s Mistress will be in Extremis and Episode 7, but now also Episode 11 and Episode 12. This is the same season finale that includes multiple versions of the Cybermen – at least Cyberiad, Cybus Industries and Mondasian Cybermen from The Tenth Planet, in-which William Hartnell’s First Doctor helped destroy Earth’s twin planet, Mondas.
A leaked season trailer from ABC (via Google Drive) shows Peter Capaldi’s Twelfth Doctor standing by a great prison door decorated with Gallifreyan text:
We also see Nardole holding the Fourth Doctor’s sonic screwdriver:
Clearly, a lot of Classic Doctor Who references are going on. But there’s something else. Because all of these things are connected. On 20th February, @GirlyLetters posted a video on Twitter of BBC Worldwide’s Showcase, specifically of costumes linked on the theme of Series 10:
As you can see, many of these can be seen in Series 10’s trailers. There is also a Sycorax helmet from The Christmas Invasion, the species matcher from Vincent and the Doctor and a broken Cyber-helmet from The Invasion. But we can also see a Time Lord ceremonial dress, a fez and the costume worn by Hartnell’s First Doctor in The Tenth Planet.
It is not a coincidence that these items can be found in a Series 10 costume display. The leading rumour at this time is that Doctor Who history is folding in on itself due to the actions of the Mistress, who intends to prevent Mondas from being destroyed and has kidnapped the First Doctor in order to steal the Doctor’s original cycle of twelve regenerations – which would thus prevent the Twelfth Doctor from coming into existence. The First Doctor is being kept by the Mistress behind the large doors, and will be revealed at the end of Episode 12 – this will lead into the Christmas Special, the third part of Moffat’s epic three-part bow. The First Doctor will be played by David Bradley, who played Hartnell in An Adventure in Space and Time. Due to the presence of Mondas, Bill will be revealed as a Mondasian, with what we’ll be led to believe is contemporary Earth in fact being Earth’s twin planet, Mondas. Whether this means Bill will be upgraded to a Mondasian Cyberman is unknown, but Bill does need to be disposed of by the time Series 11 begins.
Whether or not this is connected to Anneke Wills’ recent set visit remains to be seen, but personally, I’d say no. Lots of old cast members have visited the set in recent years. Plus, Michael Craze’s absence would need to be explained.