Mortal Shell II Steam Deck: Performance and Settings

Mortal Shell II is described as playable on Steam Deck in the available tests, but the default experience is centered on a locked 30 FPS target with occasional stutter or drops. The review also says that a graphics menu is not exposed by default, so the tested setup uses launch options and manual quality choices. Treat these settings as evidence from specific tests, not a universal performance guarantee for every Deck, Proton build, or game update.

Default behavior

SteamDeckHQ reports that the controller menu recognizes the Deck and that the default frame-rate behavior is locked to 30 FPS. The same review notes occasional stutter and drops, with mixed visual quality on the default setup. It recommends keeping the 30 FPS target for fights even though a higher frame rate may be possible in less demanding situations.

The review also reports roughly three hours of battery life during its test. Battery life depends on display brightness, power limits, game build, and other Deck settings, so the figure is a test result rather than a promised runtime. Keep it as a caveat when planning a longer session.

Restoring the graphics menu

The Steam Deck review says that the graphics menu can be restored with the launch option SteamDeck=0 %command%. Its tested setup uses Global Illumination on Medium and the TSR upscaler. Turning off upscaling has a large performance cost, so treat the option as a performance control rather than a cosmetic toggle.

Windowed Fullscreen is also reported to fix a UI issue and automatically use a 1280x720 output. That behavior may vary with later patches or display configurations. If the game does not behave the same way, remove one change at a time so the cause is clear.

Community settings snapshot

A Reddit performance test recommends Scalability Medium, Hardware Ray Tracing Off, Global Illumination Low, Shadows Medium, Anti-Aliasing Medium, View Distance Medium, Textures Medium, Visual Effects Medium, Reflections Medium, Post Processing Low, and Environment Medium. It also records FSR 4.1 on Performance. These values are a community snapshot intended to balance image quality and frame rate, not official recommended settings.

The same post records the launch command SteamDeck=0 PROTON_FSR4_UPGRADE=1 ~/lsfg %command% and the Proton build Proton-cachyos-11.0-20260702-slr-x86_64. Because that command depends on the author’s local tools and Proton setup, do not copy it blindly into another Deck. Confirm that the referenced component exists on the device before testing.

A safe testing order

Start at the default 30 FPS behavior and confirm that the game launches and controls correctly. If the missing graphics menu is the problem, test SteamDeck=0 %command% by itself, then change Global Illumination and the upscaler one at a time. After every change, test a demanding fight rather than judging performance only in a quiet menu or open corridor.

Keep the quality preset modest before lowering every individual option. The available community snapshot uses Medium for many settings, Low for heavier effects, and upscaling to protect performance. If a later game update changes the frame-time profile, keep the same method but re-measure instead of assuming the old combination remains optimal.

What to treat as a test result

These settings do not establish a universal configuration, a guaranteed frame rate above 30, or a fixed battery result. They also do not show that every Proton version works equally well. Treat the commands and values as review or community observations, then re-test after changing one variable.

Steam Deck testing cannot substitute for official Windows requirements. Use the separate system requirements page for CPU, GPU, RAM, and storage information.