The first one, "Space Babies" was alright, but felt too childish. "The Devils Chord" didn't hit for me because they just didn't have the budget for really being able to explore a higher level being of such power.
But Boom? Boom can be defeated by one simple question. "Where's the Sonic?"
It's never addressed, the Doctor never asks Ruby to go get it from the TARDIS if he doesn't have it on him. And it's never even explained that if she could go and get it, it wouldn't effect the landmine.
It's basic questions like this, that need to be answered in an episode like this. It would have taken a total of 4 sentences to cancel out the Sonic. But they never even mention it.
That's just bad writing right there.
Plus the Doctor's dialogue felt like it belonged more to Matt's Doctor than Ncuti's and DEAR GOD, Moffat cannot write children to save his life.
I'm hoping the season gets better because they're 1.5 for three with me right now.
They did explicitly explain the catching of the tube with putting the foot down though.
Although how funny would it have been to make him do the episode on one foot? ;)
But it doesn't explain the sonic.