Supplies are rare and valuable in Metro: Last Light, with gas masks being absolutely essential, most weapons cobbled together from various parts, and ammo scarce enough to actually become the currency of the subways. Light and shadow are also key to the action, with players using a hand-crank flashlight, a lighter, and torches to illuminate dark corridors and keep mutants at bay, while a special wristwatch lets them know how much oxygen they have and if enemies can see them. Gamers carry three customizable guns at a time, and while the action is linear, players can often choose to engage in direct assaults or use stealth to sneak past trouble zones.