Dreams of a masquerade represent secrets, mystery, tricks, manipulation and that you are exploring different dimensions of your being and are playing a role. See Mardi Gras, Mask and Halloween.... Strangest Dream Explanations
If you dreamed of attending a masquerade ball, where everyone was in costume except you, this is a warning against false friends.
To dream that you are wearing a costume, signifies that you are putting on a false face toward others. Your true self is not being revealed and you are not being completely honest with people around you.... My Dream Interpretation