Other mistake: Anna is shown from the front as she ascends an ice staircase inside Elsa's ice castle. There are giant ice pillars to Anna's right and left. They should reflect the side of her face, but instead the reflections show her face from the front.
Suggested correction: That's not how reflections work. The ice walls are about two feet to her side so the reflection would look like it was shot from the front but about 4 feet to the side.
Other mistake: In the scene where Marshmallow is chasing the characters off the cliff, Olaf falls first, followed by Anna, then Kristoff last. At the bottom, Anna created a mound of snow where she fell, yet Kristoff managed to get underneath pristine snow, and Olaf.
Other mistake: When Elsa is about to get shot, Hans, from where he was, couldn't have possibly got to the guard in time.
Other mistake: When Anna's horse gets scared and runs off, Anna falls into a stream and gets soaked. Trouble is, everything else in the kingdom is frozen solid - the sea, waterfalls, etc. - there's no way that stream would still be liquid.