Ruby has a woman who stands 73 yards away from her and every time someone Ruby knows talks to that woman they becomes terrified and/or run away and want nothing more to do with Ruby.
I'm not sure there are as many impossible things that are completely separate from each other as people think in this episode, they're all connected to the central premise surely?
And by that rule don't most, if not all, Doctor Who episodes feature multiple impossible things?
The Doctor is 2000 years old: Impossible.
The Doctor is an alien: Impossible.
The Doctor has two hearts: Impossible outside of a conjoined twin.
The Doctor's entire body can regenerate at a cellular level making him look completely different: Impossible
The Doctor has a machine that can take him anywhere in space. Impossible.
The Doctor has a machine that can take him anywhere in time. Impossible.
Even if you conflate the first four points and the latter two points you still have two impossible things, and that's before the Doctor opens the door of the Tardis and meets a stone statue that can transport you back in time (Impossible) or a race of xenophobic mutants who exist in self propelled tanks (impossible) or an alien who's splintered his consciousnesses throughout time (impossible) or even an impossible girl who's splintered her consciousness throughout time
Don't get me wrong, the 'one impossible thing' is a very good storytelling tenet to follow, I'm just not sure it's something that can be necessarily applied to an ongoing show like Doctor Who that's entire premise is based around things that are essentially impossible.