Difficulty mode

The Japanese version of Metroid Fusion features an Easy Mode and Hard Mode. The North American version, which was released first, does not; the Easy Mode was likely added in response to complaints about the difficulty. Metroid: Zero Mission is the first 2D Metroid to feature multiple difficulties in the Western version of the game. In both games, Easy and Normal are available by default while Hard is unlocked by completing the game on Normal.

In both games, Hard Mode also affects expansion tanks, reducing the amount that they expand Samus's arsenal. Energy Tanks only provide 50 units of energy (half of their usual 100), Missile Tanks only expand Samus's Missile Gauge by 2, and Super Missile and Power Bomb Tanks only add one additional unit. In Zero Mission, harder difficulties have shorter time limits during the escape sequences.

In Metroid: Other M, Hard Mode is unlocked after achieving 100% completion. On top of increasing damage dealt by enemies, it removes all expansions in the game, essentially constituting a 0% run. This makes Samus especially vulnerable and some boss attacks can result in instant death.

In Metroid: Samus Returns, a unique difficulty mode is unlockable via the Metroid amiibo: Fusion Mode, which changes Samus's Power Suit to the Fusion Suit. This difficulty level is significantly harder than Hard Mode, which is unlockable in the base game after completing it once, as it increases enemy damage by four times as much as what it is on Normal Mode.

Metroid Dread initially had only Normal and Hard Mode difficulties, but a free update released on February 9, 2022 added Rookie Mode and Dread Mode. The former is an easier difficulty that increases the amount of energy recovered among other changes, while the latter is a harder difficulty where Samus dies after a single hit. A second update on April 7, 2022 added a Boss Rush mode, which can be played on either Normal Mode by default or on Dread Mode.

Metroid Prime is the first game to feature adjustable difficulty levels worldwide. Upon completion of the first playthrough on Normal Mode, Hard Mode is unlocked. Metroid Prime 2: Echoes and Metroid Prime: Federation Force continue this trend. Unlike the 2-D games, harder difficulties in the Metroid Prime trilogy reduce the damage Samus deals. Hard Mode also affects some of the Federation Force Campaign mission score bonuses, such as increasing the amount of points needed to be scored, or lessening the par-time.

Metroid Prime 3: Corruption introduces Veteran Mode, an "intermediate" difficulty, and replaces Hard Mode with Hypermode. New Play Control! Metroid Prime and Metroid Prime 2: Dark Echoes, as well as the Metroid Prime Trilogy, apply the Veteran and Hypermode difficulties to the first two games as well, although the New Play Control! games still refer to the latter as Hard Mode. Hypermode is the same as the original Hard Mode, while Veteran is comparable to the Normal Mode of the original games, and an even easier Normal Mode is added. In Metroid Prime Remastered, the easiest difficulty level is now named Casual, with Normal and Hard replacing Veteran and Hypermode respectively, mirroring the original GameCube versions.

Metroid Prime Pinball features Expert Mode, which increases the difficulty of Mini-Games from level 1 to level 2 on the first play. Metroid Prime Hunters is the only Prime game to not have an adjustable difficulty setting.