When first meeting David, Princess Anna tells him that her name is Joan. While Princess Anna is singing her first song in Frozen (2013), she says to a painting, "Hang in there, Joan."
Elizabeth Mitchell appeared on Lost (2004), which was also written by Edward Kitsis and Adam Horowitz.
This is the second time Jennifer Morrison and Elizabeth Mitchell are working together. Elizabeth Mitchell guest starred in Damned If You Do (2004), in which Jennifer Morrison was in the main cast.
When Emma and Elsa are in the ice cave, Emma says she is freezing and asks Elsa if she is cold. Elsa tells her the cold never bothered her. This is almost identical to a line in the son Let It Go, from the movie Frozen, where Elsa sings "Cold never bothered me anyway"