Tagging this while not knowing half the pokemon was abseloute hell and I'm not doing that. I spent SO FUCKING LONG trying to find klefki because I didn't see the keys and kept looking at the "head and arms" section of pokemon by shape.

Adding tag: abra (reading book below the middle ladder) and unown (on the bookcovers).
There's also something peeking down from the bookshelves (circled by Mew's tail) which is too low-detail to identify.
Edit: from the shape it's bronzor but still too low detail to put into taglist.