There were so many times in the movie where I felt I was rewatching scenes from some other movie. The death of the horse literally had me whispering "Artax! No! Don't give in!" to my friend next to me. The landscape/traveling scenes with their brief epic music wouldn't be out of place in LotR, the Dark Forest reminded me of every fantasy movie ever - though particularly Princess Bride - and the forest spirit had wandered over from Princess Mononoke and was pretending to be Aslan on the set of Avatar.

The Dark Forest stuff, I think was... when she falls in the forest, there's like a release of spores from the ground? I think that was supposed to be the origin of her hallucinations. And the mirror is either self-delusion or simply metaphorical. The queen is obsessed with beauty, so her mirror literally tells her what to do.