Expansion



An expansion or tank is a form of power-up that increases the amount of ammunition Samus can carry, or her Power Suit's energy levels, or otherwise enhances her abilities. Expansions are abundant throughout the worlds of the Metroid series. While Samus is never required to collect all expansions in order to complete her missions, doing so can make later confrontations much easier. Recent titles of the series also provide rewards for collecting all expansions.

Energy
A notable example of a Power Suit expansion is the Energy Tank. Each Energy Tank collected increases the amount of energy Samus can carry by 100 units and fully restores her energy on the spot. Traditionally, she can carry up to 14 of these. On Hard Mode in Metroid: Zero Mission, an Energy Tank only adds 50 units of energy; Samus must then collect a second to form a full tank.

In Super Metroid and Metroid: Samus Returns, Samus can use Reserve Tanks to store excess energy. In the event that her Power Suit's energy is depleted, the Reserve Tank will automatically replenish her energy by four tanks in Super Metroid, and one in Samus Returns. This can only be used once in an enemy encounter. Energy Reserve Tanks can be acquired in Super Metroid, while in Samus Returns they are unlockable through scanning the Samus, Zero Suit Samus and Samus Aran amiibo. These also unlock Missile and Aeion Reserve Tanks.

Metroid: Other M introduces Energy Parts and E-Recovery Tanks. Only a few whole Energy Tanks can be acquired in the game; the rest have to be assembled through collecting four Energy Parts. This is similar to the decrease in provided energy from Energy Tanks in Zero Mission on Hard Mode difficulty. E-Recovery Tanks increase the amount of energy Samus can recover through Concentration by one tank.

In Metroid: Samus Returns, there are Aeion Tanks that increase Samus's Aeion Gauge by 50 units. Like Energy Tanks, Aeion Tanks fully restore Samus's Aeion. She can collect fifteen of them during the SR-388 incident.

Ammunition
By far the most common expansion that can be found is the Missile Expansion, or Missile Tank in the non-Prime games. These appear as floating, sometimes glowing missile pods that increase the Missile Counter, traditionally by 5 units (although in Hunters, Other M and Samus Returns they add 10, 1 or 3 extra missiles). Every game that features the Power Bomb, with the exception of Other M, also features expansions for it. In Other M, Power Bombs are unleashed by charging a regular Bomb in Morph Ball form.

Super Metroid, Metroid: Zero Mission and Metroid: Samus Returns feature Super Missile Tanks that increase Samus's Super Missiles by 5 (Super), 2 (Zero Mission) or 1 (Samus Returns). This tank does not exist in the Prime series or Metroid Fusion, which instead feature the Super Missile as an upgrade over the regular Missile Launcher, and it uses Missile Ammo. In Metroid Prime 3: Corruption, Samus can acquire expansions for her Ship Missile Launcher, allowing her to carry up to eleven Ship Missiles if she collects them all. Corruption contains a reference to an unused expansion for the Ship Grapple Beam, although how it would have worked is unknown.

While most Beams in the Metroid series have infinite ammunition, Metroid Prime 2: Echoes and Metroid Prime Hunters introduce Beam Ammo and Universal Ammunition (UA), with the Dark, Light and Annihilator Beams and the six Affinity Weapons functioning through replenishable ammunition. In Echoes, Samus can collect four Beam Ammo Expansions that increase her capacity by 50 units. In Hunters, UA Expansions increase her capacity by 30 units and Samus can collect 11 of them.

Other M introduces a Charge Meter for the Charge Beam, and Samus begins the game with a slow rate of charging. Six Accel Charges collected throughout the game can shorten the charging time by 0.5 seconds per charge. If Samus collects them all, charging will only take half a second for her. Accel Charges have no effect on the charging rate of Power Bombs or the Paralyzer. In all other games, charging is automatic and the speed cannot be increased or decreased.

Other
While not technically expansions, "key" items in the Prime Series are included with expansions in the Inventory. Keys include Chozo Artifacts, Alimbic Artifacts and Octoliths, Dark and Sky Temple Keys, and Energy Cells. With the exception of the latter, Samus is required to collect all of these keys in order to reach the Impact Crater, Oubliette and Sky Temple. Only a certain amount of Energy Cells are required to access the Control Room aboard the G.F.S. Valhalla, and acquire the codes that will allow the Galactic Federation to reach Phaaze.

Rewards for collecting expansions
All three games of the original Metroid Prime Trilogy, Metroid: Other M and Metroid: Samus Returns provide rewards for collecting percentages of expansions. Most often these are Concept Galleries, unlockable galleries of concept art for the game. In Samus Returns, the Chozo Memories are unlocked by collecting all expansions, with a new memory being unlocked for every 10% of items collected.