Bistable vibration energy harvesters have been used to achieve strong energy harvesting performance over a wide frequency bandwidth. Performance of bistable energy harvesters is dependent on whether the external excitation is large enough to surpass the minimum threshold to high energy, or ‘snap through’ oscillations. Studies have indicated that lowering the potential energy barrier via an auxiliary unit is an effective way to ensure that high energy orbits are achieved. Recent advancements have shown that directly extracting energy from an auxiliary unit used to dynamically lower the potential barrier of a bistable energy harvester can enhance performance. However, there remains an unexplored opportunity for further improvement by incorporating nonlinearity into the auxiliary harvesting element. Thus, to advance the state of the art, this research introduces an energy harvesting system composed of a bistable cantilever harvester magnetically coupled to an auxiliary nonlinear harvesting element. An analysis of the system potential energy indicates that the additional nonlinear characteristics of the coupled harvesting element can enable tailoring of the potential energy profile such that quad-stability, or multi-directional bistability, can be achieved. Investigation of the quasi-static potential energy trajectory of the proposed device indicates that the number of stable states, height of the potential energy barrier, and snap through amplitude may all be tailored through consideration of the effective linear stiffness of the nonlinear harvesting unit. Numerical simulations of the system dynamics indicate that the additional nonlinearity incorporated into the coupled system improves broadband harvesting performance.