I liked the episode. It wasn't great but wasn't bad, and it was a little rushed.
The celestial body that the monster possesed was a gas giant, not a star. The individual little planetoids were actually satellites, moons if you prefer. There was atmosphere between the moons, like a huge sky with islands floating in it. The closest analogy I've seen was the Flash Gordon movie in 1980, when all of the moons of Mongo and everything in between had air and clouds.
And when the entity was defeated the planet was still there, just like it was before it popped out of the pyramid and flew to the planet. Gravity and atmosphere was not disrupted.
How could anybody think they were flying that little scooter through outer space? There was wind!
Forgive me for going wibbly-wobbly on everyone here, but might we have just witnessed the birth of the Great Intelligence? The Doctor poured all his memories into it, but it wanted more. So Clara gave it all the things that could have been, but weren't, and then it ... what? Vanished? Died? Went somewhere else? Somewhen else?
I like it! The GI and Clara might have some link between them.
I also wonder if it somehow connects to The Dream Lord, they really never explained where he came from.
Yes, there was pollen in the Tardis or some such explanation, but I think there could be more.
Why would the TARDIS have a problem with River? The only real reason her story is complicated is because the Doctor always meets her in the wrong order. There is nothing inherently problematic about her existence.
My point was relating to something someone said about Clara being a threat to the Doctor, and clearly River was, technically, a threat to the Doctor as well!
Clara's impossiblility might be a theat to the Tardis somehow. River obviously was a threat to the Doctor, but they got along great. The Tardis didn't want any part of two Amys, so infinite Claras would probably be worse.