higher, further, faster, baby...

Bill is the Doctor's younger self if he'd actually gotten to self-actualize as a teen/twentysomething autistic lesbian. She gets sabotaged by Saxon Master, who self-destructs rather than become a woman. Missy and Bill are again two faces of the "self" - Missy as the self subject to a literal suicide, and Bill as the young-lesbian-self, spiritually smothered, forced into the ultimate mask/closet of cyber conversion. (This is the culmination of the themes we've been setting up since deep breath, re undeath, turning yourself into a literal or emotional robot in order to survive, killing the true parts of yourself so many times that you've ship of theseus'd your "self" out of existence and all that's left to you is to jump or be pushed, etc). And yet, Bill can't be extinguished. Where there's tears, there's hope. The Doctor has to face both the younger self who was (oh god I said so much sexist shit when I was younger, I'm going to throw up), and the younger self who never was (Bill, the self beneath the robotic mask). The Doctor has to grieve Bill, and yet understand that she's still there. She never really died. Despite your best efforts, despite the machine you tried to turn yourself into, the living death you made of your life...that inner spark survived.

"You want some?"