While talking to Bill in the barn, The Doctor offers a little girl Jelly Babies, which were a favorite of the Fourth Doctor.
This episode removes any contradiction that had previously revolved around the various Cybermen origin stories, by having the Doctor call all instances parallel evolution.
This was meant to be the end of Steven Moffat and Peter Capaldi's tenures, with Chris Chibnall expected to take over in the Christmas special. Moffat later learned that Chibnall actually planned to skip the special and that the BBC wouldn't commission any more Christmas specials if one were skipped and the annual tradition abandoned.
This is the first season finale in the revived series and the only episode of season ten to feature no scenes on present-day Earth.