(Home instance is having federation issues, so reposting some comments on this account. Apologies for dupes.)
That was nice! Wasn't a huge fan of the musical number, but it was fine. Feel like I'm still struggling to get a good feel for 15's vibe, but it seems good overall. Ruby and her family are great. Mavity is still a thing and I wonder if "Coincidence" is going to be a theme with these two.
Also, that stinger! Some character that breaks the 4th wall? That's new. Was it her hand at the end of the last episode? I'm going over the scenes with her in my head and just have more questions XD
With a name like Mrs. Flood, I'm half expecting a link to either River Song or Mars. Is her first name Carol? Probably not, considering that's a Moffat character.
"Waters of Mars" was a Davies joint, but maybe the name is just a coincidence (!), along with the fact that that story took place on Bowie base, named after the man who played a goblin king who steals babies (!).