|Tangerine Dream. I'm so sorry.|
It's not a trope, but mad props for including a visual reference to Cocteau's avant-garde film Orphee (Clara standing still as the background recedes behind her, which happens in Cocteau's film when characters journey through the underworld).
A Thing in a Thing: A dream in a dream in a dream in a dream in a dream.....
The Doctor is A: Dream.
The Master Is A: Dream.
Clara Lies About: In a totally foreseen development, Clara and the Doctor find out that they lied to each other last episode.
Reasons Clara Should Drop Danny Like A Hot Potato: Because, although the dream-Danny we meet is a complete gent, he is, as he himself points out, dead, and not going to come back.
Child Count: One (briefly).
The Thick of It: Didn't spot anything, but Red Dwarf would like a word.
It's Actually About: The tangerine on the windowsill at the end of the episode, and the Doctor “waking up” by the volcano from “Dark Water” shortly beforehand, indicate that we're still in a dream (a tangerine dream, presumably), and the fact that Santa Claus turned up in the Tardis at the end of “Death in Heaven” indicates that we have been in a dream for some time. Therefore, a certain percentage of Doctor Who, and potentially all of it, is actually a dream. This, consequently, not only retroactively makes sense of all the daft ideas and continuity problems that have gone before, but effectively insulates the entire series against future snarking. So much for this column, then.