"Magician's Apprentice" what?
C'mon, you know the story even if you've only ever seen the sequence from Fantasia ... Mickey Mouse is the magician's apprentice, bored with carrying buckets of water, so he goes to the forbidden Teach Yourself Spelling book (a volume which I can recommend to many of my fellow commentards...) and changes a broom into an automaton to fetch and carry for him; but matters get out of hand, with hundreds of automata, and flooding.
Let's select some events we saw and arrange them in timeline/parachronological order...
(*) The fourth Doctor discusses "What would you do if a child you saved became a dictator responsible for the deaths of millions?"
(*) The current Doctor finds he's encountered that dilemma, and he leaves Davros to die
(*) Clara and Missy get zapped
(*) The current Doctor returns that dilemma, or close nearby, and threatens to kill Davros himself
(*) If the Tardis has been destroyed, how did the Doctor return to Skaro bearing a Dalek weapon?
(*) How did the Doctor find himself being manipulated into saving Davros in a way that leads to Davros creating the Daleks?
(*) The fourth Doctor chose not to destroy the Daleks saying that much good had come about because they'd existed, and there would be other opportunities to stop them ... has he set himself up with an opportunity?
I'd say: the Doctor has broken one of the fundamental rules, he's returning to an established timeline to change events, and there will be a spew of events that get out of hand, and causality paradoxes galore. He wants to change events so that Clara and Missy do not die, and defeating the Daleks is a handy pretext to justify changing events. We've seen Clara in scenes pre-series trailers that we haven't seen yet; there will be more Clara, for a bit at least. I'm guessing we shall see the origin of the Impossible Girl, but, eventually, the Doctor will have to choose between letting Clara die and destroying time itself.
Of course, all this is good for those of us wanting the lid to pop off the Time War, because then somehow we get both more Daleks than you can count, and the return of Gallifrey and the Time Lords -- except we won't, because that's the special sauce Moffatt uses to keep us wanting, and anyway there isn't the budget.
I'd also compliment the production crew for the sets and sound effects ... Dalek architecture, ambient ticking noises etc are present as per both the DVD releases of Hartnell-era stories and the recent "An Adventure In Time And Space".