For variable oscillation mechanisms, if output stroke is decreased, output-link force will increase for a same input due to the mechanical advantage. Thus, in order to eliminate input actuator stall phenomena for cases where sudden increase occurs at output load, variable oscillation mechanisms can be employed. In this study, a novel design procedure for seven link two degree-of-freedom variable oscillation mechanisms is proposed. The mechanisms run as a six-link mechanism for a fixed position of a control-link. With this method, a variable oscillation mechanism is designed. It is shown that the design procedure is consistent by performing a kinematic analysis. Also, an approach to switch to second oscillation mode is introduced via underactuation. Finally, it is verified that the theoretical approach proposed is consistent for underactuated switching with Nastran simulation.