As the Missy>Mistress>Master was guessed fairly quickly by a lot of the fandom, surely Moff must have known this. Why, therefore, wasn't Missy's name just kept as Michelle Gomez's original role as Gatekeeper of the Nethersphere?

It would've prevented everyone guessing the twist and, I believe, retained the same amount of mystery and intrigue surrounding the character.

Perhaps I'm missing something but I'm surprised that Moffat didn't say that the title of Missy was too obvious, with Gatekeeper of the Nethersphere being much more vague and subtle. What do you think?

I think it worked quite well actually. For casual viewers who don't think about this kind of thing too much, it would have been a good reveal, along the lines of 'oh yeah, missy>mistress>master, cool' whereas for the fandom, it was a clue so hidden in plain sight that many people on here were suggesting that whatever missy was she would definitely not be the master just because such a thing would seem so obvious.

Basically it cleverly fooled both type's of fan one way or another.

Perhaps he made it obvious SO we would work it out easily.

That way, the concept could settle in amongst the fandom for a while, and lessening some the impact to anyone who might have been outraged by changing the Master's gender.

One of the arguments against changing The Doctor's/Master's gender, is that its just a stunt to shock everyone and get views. If we expected it, you could hardly use that complaint.

Or maybe he just went for a simpler twist just for a change. Could be over-thinking it. Then again, Deep Breath was meticulously constructed as one big guilt trip forcing people to accept an older Doctor.

It was actually such a fairly obvious reveal that people started to doubt it could be the Missy > Mistress > Master scenario.

Ha, yes, I didn't think it could be a double bluff. Very interesting, thank you.

I quite like the thought of Missy being the Master but what if Missy is acting as a decoy & the real Master is her assistant Seb? Can't claim it to be my idea, my son suggested it because Seb has some similar personality traits to John Simm's Master. It's certainly a point worth considering?

They've made her so like the master, i'd be disappointed if they were to backtrack on the point now. I am definitely interested in finding out more about seb though as he blatantly understands all of what is going on, and seems to be enjoying himself every bit as much as Missy, so whoever he is, he must be evil like her.

My guess is Seb (like Gus was) is the Computer.

Could be, we have yet to see him outside the 'nethersphere'

In some promo shots she looks like a female version of Capaldi's Doctor, which works wonderfully.

Seb could either be a real dead person that just happened to be compliant, unquestioning and good at admin, or a construct of the Matrix. He may just be a facade, like Mr. Popplewick in Trial of a Time Lord (disclaimer: only going by descriptions, haven't watched that episode in a long time.)

I'm thinking SEB: Someone Else's Brain (or Body maybe?)

a nod to Douglas Adams SEP field

Yep. Had me fooled. My first thought was to draw the conclusion that Missy = Mistress = Master, only to immediately discount it as being too obvious. Another example of Moffat's love of hiding answers in plain slight, this time using a simple double bluff.

I'm another who thought that Missy / Master link was too obvious, especially knowing Moffat's love of complexity. I called that one wrong!

Be a dull place if we were always right, eh?

He might of as well called the episode the return of the master .

Way back in time in classic Who The Master was hidden under the name of Reverend Magister in The Dæmons. Many didn't see that coming so is this a Moffat nod to history?

http://en.m.wikipedia.org/wiki/The_Dæmons

Huh? The first time we see Rev Magister it's clearly Roger Delgado. As I remember we even get the little Master musical motif. So you can't really say that no-one saw that coming. Also, the Master had been in every story that season and was credited in Radio Times. Not really hidden...
Better 'no-one guessed that it was the Master' scenarios might include a number of the 80s Master stories where his involvement was hidden from the public by the use of anagrams of Anthony Ainley's name on the credits.

Seb is the RANI