Some missions will require that a "Gold Box" emoji be used. In these cases, you would have to use an emoji that was actually collected from a Gold Box.
Although Villains like Ursula, Jafar and Maleficent can be pulled from the Gold Box, they are Villain emojis (purple border) and are not able to complete such missions.
For a list of emojis and their types, see "What are the different types of emojis?"