Magnesium-sulfur (Mg-S) batteries typically exhibit high discharge capacity but suffer from poor cycling performance due to the shuttle effect of polysulfides. In this study, we develop an artificial electrode skin on the SeS₂ cathode in a Mg-SeS₂ battery to effectively suppress the shuttle of polysulfides and polyselenides. A range of electrochemical and spectroscopic characterizations are conducted to investigate the confinement effect of the i-MXene-based electrode skin on dissolved sulfur- and selenium-based species. Theoretical simulations indicate that surface hydroxyl groups and other functional moieties of i-MXene can effectively confine active species to the cathode side. As a result, the Mg–SeS₂ battery with the cathode skin layer demonstrates a high discharge capacity of 750 mAh g⁻¹ at a current density of 0.1 A g⁻¹, with excellent cycling stability. The battery maintains 76% of its capacity after 100 cycles at 0.5 A g⁻¹ and 62% after 300 cycles at 2 A g⁻¹, exceeding or matching the performance of most previously reported Mg–S batteries. This work demonstrates a viable strategy to boost the electrochemical performance of Mg-ion batteries.