The Doctor and Clara find themselves in Victorian London with a temperamental Tyrannosaurus Rex and a spate of spontaneous combustions. There are Clockwork Robots up to no good and the Doctor is doing the usual post-regeneration amnesia thing. Clara doesn't understand the regeneration process and misses Eleven. Vastra and Jenny call her a cunt and the three of them mudwrestle in dissolving bikinis for the rest of the episode.
Deep Breath serves as Matt Smith's last known photograph.
Deep Breath (among others) was leaked online as a black-and-white workprint with incomplete CGI and music. Ah, it was a glorious time. Leak /who/ was fantastic. May the words "Prepared for Marcelo Camargo at Drei Marc" never be forgotten.
The episode has an extended runtime of 76 minutes.
The Doctor goes Scottish.
Capaldi's eyebrows can remove bottletops.
After seeing his new face for the first time Twelve wonders why it seems so familiar, referencing his appearance in The Fires of Pompeii.
Still waiting to see where that plot arc goes - didn't RTD and Moff have some kind of masterplan for it? MOFFUCKED
In his post-regeneration confusion, Twelve thinks Clara is a regenerated Handles (and isn't impressed). He also thinks that Strax is one of the Seven Dwarfs. He's probably correct.
Twelve leaves Clara to die. He rescues her of course, but that's beside the point.
Twelve becomes addicted to chalk.
Stevie Moffatino joked that Matt's cameo was the fastest return of a Doctor ever. Apart from the TV Movie, this was the first time a previous Doctor made a substantial appearance in the first episode of his successor's era.