A stepchild might be singled out for abuse. But a red-headed stepchild (who presumably looks like his or her absent birth-parent) might be abused even more because he or she is so obviously different from the other children.
A bashling. Some one who is singled out for emotional abuse and/or physical abuse. Some one who gets purposely written out of their inheritance. Some one with no birth rights. Some one purposely neglected financially. The unfavored one.