Two-dimensional (2D) altermagnets (AMs), characterized by distinctive spin splitting and robustness against external fields, have emerged as promising candidates for spintronic device applications. Exploring multipiezo effects in 2D AMs through precise and energy-efficient modulation strategies has become crucial for realizing their multifunctional applications. In this work, we demonstrate that the $\mathrm{F}{\mathrm{e}}_2\mathrm{Mo}{\mathrm{S}}_2\mathrm{S}{\mathrm{e}}_2$ monolayer is a 2D AM with a pronounced spin splitting of 0.45 eV for valence bands. The $\mathrm{F}{\mathrm{e}}_2\mathrm{Mo}{\mathrm{S}}_2\mathrm{S}{\mathrm{e}}_2$ monolayer exhibits valley degeneracy at the ${\mathrm{X}/\mathrm{X}}^{\prime }$ valleys, which is protected by $\left[C_2\parallel C_{4z}\right]$ and $\left[C_2\parallel M_{xy}\right]$ symmetries. Uniaxial strain as an energy-efficient modulation strategy breaks the balance of these symmetries. This imbalance induces piezomagnetic and piezovalley effects in $\mathrm{F}{\mathrm{e}}_2\mathrm{Mo}{\mathrm{S}}_2\mathrm{S}{\mathrm{e}}_2$ monolayer, accompanied by the emergence of an anomalous valley Hall effect. Furthermore, $\mathrm{F}{\mathrm{e}}_2\mathrm{Mo}{\mathrm{S}}_2\mathrm{S}{\mathrm{e}}_2$ monolayer possesses a Janus structure, which enables significant in-plane and out-of-plane piezoelectric effects under uniaxial strain. The multipiezo effects make the Janus $\mathrm{F}{\mathrm{e}}_2\mathrm{Mo}{\mathrm{S}}_2\mathrm{S}{\mathrm{e}}_2$ monolayer a promising platform for the development of multifunctional spintronic devices.

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• Ferroelasticity
• Magnetic phase transitions
• Piezoelectricity
• Valleytronics