When the Snow Queen is transported in to modern world in 1982, an add for "Tron" is visible on the street, which came out in 2010.
The Snow Queen tells Mr. Gold that she now wields "the magic of my three sisters." However, she has only two magical sisters, Elsa and Emma, so what she should have said was "the magic of my two sisters" or "the magic of three sisters" (the latter meaning herself and her two sisters).