Mechanical metamaterials refer to engineered materials having previously unachievable mechanical properties that are defined by their microstructural architecture rather than their composition. Based on our expertise in micro additive manufacturing and soft materials, we explore novel multifunctional mechanical metamaterials that can exhibit tunable physical performance through active transformation of micro-architectural elements. Physical properties of metamaterials consisting of repeating unit cells are strongly dependent on spatial layout and deformation mode of microstructures of unit cells. Therefore, active and reversible switch of geometry will lead to a significant modulation in target physical properties. For example, a rigid structural material can instantaneously change to a compliant energy absorbing material through transformation of unit cells from the stiff configuration to the soft configuration. The innovative multifunctional thermo-mechanical metamaterials will inspire a broad range of engineering applications such as tunable shock absorbing protection, active impact mitigation, and adaptive thermal managing interface.