I started to think that Missy would do what she did, since she said that she couldn’t remember all that much about her regeneration. It doesn’t exactly line up with the Master’s whereabouts during the Time War (considering that Missy most likely made it off Gallifrey by going through the 3D painting in the Black Archive during the 50th anniversary special), although it’ll all fall under the “timey-wimey” label.
Bill’s rescue seemed a bit too ‘deus-ex-machina’, but I’m glad to see she survives. And I’m really upset that we’ve seen the last of Missy, although I would wager it’s not the last of the Master since he’s come up with so many ways to preserve his life in the past.
And a great stinger at the end. The Doctor teams up with The Doctor. And I was guessing he might be pulling a Tennant and trying to keep from regenerating. It seems that regeneration is more traumatic than we’ve thought of it in the past. Which makes Romana’s regeneration just for the sake of looking more fashionable makes her seem fairly psychotic viewed through that lens. Or maybe it’s just the older you get, the less likely you want to change.
Now that I think about it, Missy must remember that she was previously killed by her future incarnation, and armed with that knowledge she must have prepared to get shot in the back by her previous incarnation. I would think that she’d have some kind of energy-absorbing armor lining her jacket or something. She’s had years to prepare for getting shot in the back, after all. She managed to keep from being disintegrated by Cyberman Brigadier Lethbridge-Stewart, she has a long history of extending her lifespan. In other words, I want Missy to come back. Gomez is just too damn entertaining in the role. She comes across as menacingly comedic. That’s a hard one to pull off, and she’s so much fun to watch.