This invention refers to a costume apparatus for enabling a user to engage in role play activities or action play adventures. The costume apparatus may be mounted on a user's back, and comprises deployable arm assemblies which are controlled by a pull cord system. In one embodiment, the costume apparatus takes the form of expandable wings. The arm assembly of the costume apparatus may include two arm pieces connected by a pivoting joint, and may further include a hinged joint within one of the arm pieces. The hinged joint provides a safety feature for the deployed costume apparatus by allowing the arm assemblies to fold rearward when obstacles are encountered.