Quick answer
Night Mode is an optional difficulty layer, not the default time-of-day cycle. Full-release gameplay shows the Gloombound Flame tied to enabling it, and Night Mode can expose tougher encounters/rewards that do not behave like normal daytime exploration. Balance details are still moving after launch.
What Night Mode is for
Night Mode is the “turn the challenge up” side of Mortal Shell II. It changes the world presentation and increases encounter pressure rather than simply offering a menu difficulty slider.
Full-release players have reported tankier/harder enemies and additional night-specific content in parts of the world.
How it unlocks
Full-release gameplay footage shows the Gloombound Flame as the key item associated with Night Mode. The item is obtained through an early boss/encounter path and then used through the hub/night system.
Because exact trigger order can vary with open-world routing, this page does not claim a single unavoidable quest sequence for every player.
Why you should not leave it on just because it exists
Night Mode is useful when you deliberately want its challenges or rewards. It can also make ordinary exploration slower and visibility harsher.
If your goal is simply to finish a quest, reveal map fog or reach a Shell, normal mode is usually the more efficient environment unless that content specifically requires Night Mode.
Balance Patch 1 warning
The developer/community Balance Patch 1 post says planned future updates will expand or adjust features including Night Mode, Tarstones and PP Items. That makes old “final” Night Mode build advice especially fragile.
Use this page for the mechanic. Use the Updates hub before copying exact farming or damage recommendations from launch-week videos.