Low Percent Run

A Low Percent Run is a term that refers to a playthrough of a game where the objective is to collect as few required upgrades as possible and complete the game. This usually involves utilizing many Sequence Breaking tricks or glitches to skip major upgrades or expansions, and is often associated with speedrunning, where people attempt to complete a Low Percent Run of a game in as little time as possible.
In the Metroid series, generally, no Energy Tanks are acquired if the player is going for the lowest possible percentage, though some games like Super Metroid make exceptions. Some, like Super Metroid and Metroid: Zero Mission, also have options for ammo upgrades, as multiple of some ammo type is needed to progress.
Occasionally the lowest percentages are version specific, as some tricks are taken out in later versions of the game, most notably in the Metroid Prime Trilogy.
==Minimum percentages==
===Metroid: 3% ===
*Maru Mari
There is no item percentage displayed in-game, though each upgrade rounds up to 3%. Defeating Kraid and Ridley will grant 75 Missiles each.
===Metroid II: Return of Samus: 9% ===
*Bombs
**Required to get around and defeat the Queen Metroid.
*Ice Beam
**Required to defeat the Metroid larvae.
*Energy Tank (1) or Varia Suit
**Required to survive against the Queen Metroid.
Samus starts the game with the Morph Ball, 30 Missiles, and the Long Beam. Like in Metroid, there is no item percentage and each upgrade rounds up to 3%. There are 36 total when all four interchangeable beam upgrades are counted as one.
===Super Metroid: 14%===
*Morphing Ball
*Bombs
*Missiles and Super Missiles (4 total) (2/2 or 1/3)
**Required to open Red and Green Hatches and destroy Mother Brain's Control Capsule.
*Varia Suit
**Required to reduce the damage done by Mother Brain's Laser Brain Attack.
*Energy Tanks and Reserve Tanks (3 total) (1/2 or 2/1 or 3/0)
**Required to survive the Laser Brain Attack.
*Power Bombs (1)
**Required to open Yellow Hatches.
*There are twenty different routes for the final 3 upgrades: 
**Charge Beam + Gravity Suit + Ice Beam
**Charge Beam + Gravity Suit + Speed Booster
**Charge Beam + X-Ray Scope + Ice Beam
**Charge Beam + Speed Booster + Ice Beam
**Charge Beam + Speed Booster + Grappling Beam
**Charge Beam + Hi-Jump Boots + Ice Beam
**Charge Beam + Hi-Jump Boots + Speed Booster
**Gravity Suit + 2 Power Bombs
**Ice Beam + 2 Power Bombs
**Grappling Beam + 2 Power Bombs
**Charge Beam + X-Ray Scope + Speed Booster
**Charge Beam + X-Ray Scope + 1 Missile or Super Missile
**Charge Beam + 2 Power Bombs
**X-Ray Scope + 2 Power Bombs
**Charge Beam + X-Ray Scope + 1 Power Bomb
**1 Super Missile + 2 Power Bombs
**Charge Beam + X-Ray Scope + Gravity Suit
**Charge Beam + Gravity Suit + 1 Power Bomb 
**Charge Beam + X-Ray Scope + Hi-Jump Boots
**Charge Beam + X-Ray Scope + Grappling Beam.https://wiki.supermetroid.run/14%25
***The Charge Beam is for damaging bosses due to the low ammo count.
***The Gravity Suit is for traversing Maridia and Lower Norfair.
***The Ice Beam is for skipping Zebetites, clipping Mochtroids, and climbing enemies.
***The Speed Booster is for skipping Zebetites and getting through the room preceding Botwoon.
***The X-Ray Scope is for leaving the room preceding Draygon.
***The Hi-Jump Boots routes are exclusive to the PAL version, due to the increased height gained from underwater jumps.
***The Grappling Beam is used to traverse Maridia.
***The Power Bombs are used to exploit the Crystal Flash technique in a specific manner.
A 13% TAS-only route that utilizes the Charge Beam and Speed Booster may be humanly possible.https://wiki.supermetroid.run/13%25 There are also 12%, 4%, and 0% routes that involve exploiting major glitches as well as a humanly completed 13% run without major glitches that utilizes simultaneous left + right directional inputs.
===Metroid: Zero Mission: 9%===
*Morph Ball
*Missile Tank
*Bombs
*Unknown Items (3)
*Power Grip
**Required to despawn a Tangle Vine Fruit blocking further access into Norfair.
*Ice Beam
**Required to proceed through Tourian.
*Varia Suit
**Can be skipped, but is automatically given later on after the Ruins Test, and still counts towards item percentage.
An extra Missile Tank or a Super Missile Tank must be acquired on Hard Mode, as there are two Missile Blocks followed by a Red Hatch in the Space Pirate Mother Ship, and the Space Pirates do not drop Missile Ammo. This does not apply to the PAL version, where the blocks won't respawn when leaving the room.https://www.metroid2002.com/0/version_differences_9_percent_hard.php An 8% route with memory corruption has also been completed.https://www.youtube.com/watch?v=SwEdt18JL-w
===Metroid Fusion: 0%===
No major upgrades can be avoided, but they do not count toward the item percentage. All item expansions are avoidable, although one Missile Tank in Sector 3 (PYR) is placed in a 1-tile-wide corridor, blocking the only route available. It is only avoidable through an out-of-bounds glitchhttps://www.youtube.com/watch?v=61goagsSrUo (impossible in the Japanese release), or by storing a Shinespark, going with inhuman precision to the room with the purple Geron, and using the Shinespark to destroy it in order to take an alternate routehttps://www.youtube.com/watch?v=kSn6yNuk--g.
The 1% category, which collects only this missile, is still ran due to the difficulty of the skip.
===Metroid Prime (GCN NTSC only): 21%===
*Missile Launcher
**Required to open Missile Door Locks and obtain the Artifact of Nature.
*Morph Ball
*Morph Ball Bombs
*Varia Suit
**Required to traverse Magmoor Caverns.
*Wave Beam
**Required to open Purple Doors and defeat Metroid Prime.
*Ice Beam
**Required to open White Doors and defeat Metroid Prime.
*Plasma Beam
**Required to open Red Doors and defeat Metroid Prime.
*Main Power Bombs
**Required to obtain the Artifact of Warrior.
*X-Ray Visor
**Required to defeat the Omega Pirate.
*Chozo Artifacts (12)
**Required to enter the Impact Crater.
The Phazon Suit is collected, but does not count towards the item percentage. 21% was achieved in 2010 by skipping the Space Jump Boots.https://m2k2.taigaforum.com/post/21_topic_1026.html A tool-assisted 20% route that skips the Varia Suit was confirmed in theoryhttps://www.reddit.com/r/speedrun/comments/97u9ay/metroid_prime_20_is_theoretically_tas_possible/ and eventually completed.https://m2k2.taigaforum.com/post/20_topic_576.html
===Metroid Prime 2: Echoes (GCN NTSC only)===
==== 6% ====
*Dark Beam
**Required to open portals.
*Light Beam
**Required to open portals.
*Main Power Bombs
**Required to obtain the Sky Temple Key in Dark Oasis, which doesn't exist until the Power Bomb Guardian is defeated.
*Screw Attack
**Required to reach Emperor Ing.
*Light Suit
**Required to collect Sky Temple Keys and survive against Emperor Ing.
*Dark Visor
**Required to kill the Flying Ing Caches.
Temple Keys do not count towards the item percentage. The Missile Launcher, Morph Ball Bombs, Boost Ball, Space Jump Boots, and Spider Ball are all kept due to the Item Loss Skip, where they do not count towards the percentage.
==== 4% ====
The item loss sequence has the effect of removing from the inventory all items and keys, but it also resets the percentage completion.
In a 4% run, the player must set up everything that is going to be needed after the item loss, like breaking the obstacles needed to collect an upgrade later, or killing the Flying Ing Caches without collecting their keys. Then, they will trigger the item loss while equipping the Annihilator Beam, so that it'll be still usable (albeit with no ammo) until it's switched to the Power Beam. On the fastest run at the time of writing, the collected upgrades are:
* Power Bomb Expansion
* Space Jump Boots
* Light Suit
* Screw Attack
===Metroid Prime 3: Corruption (standalone only): 15%===
*Energy Tank (1)
**The first Energy Tank is unavoidable and required to activate Hypermode.
*Missile Launcher
*Grapple Lasso
*PED Suit
*Boost Ball
*Plasma Beam
**Required to open several doors and weld panels in Elysia for the Theronian Bomb.
*Screw Attack
**Used to skip two otherwise needed Energy Cells.
*Ship Missile Expansion (1)
**Required to reach Omega Ridley.
*Energy Cell (1)
**Required to obtain the Seeker Missile.
*Seeker Missile
**Required for the Elysia Seed and to obtain the X-Ray Visor.
*Hyper Missile
**Required to access the Pirate Homeworld.
*X-Ray Visor
**Required to use terminals.
*Grapple Voltage
**Required to access the code on the G.F.S. Valhalla.
*Nova Beam
**Required to damage Omega Ridley and leave the G.F.S. Valhalla.
*Hyper Grapple
**Required for the code on the Pirate Homeworld and to progress through Phaaze.
Collecting the Seeker Missile upgrade allows Samus to fire Ice Missiles, but this does not count towards the percentage.
===Metroid Other M: 0%===
No major upgrades can be avoided, but they do not count toward the item percentage. All item expansions are avoidable. Hard Mode removes them from the game, constituting a Low Percent Run.
===Metroid: Samus Returns: 0%===
Most major upgrades cannot be avoided except for the Spring Ball, High Jump Boots, and Space Jump through regular sequence breaking and some others by going out of bounds. However, no major upgrades count toward the item percentage, and all item expansions are avoidable.
===Metroid Dread: 0%===
Item expansions are the only items that count toward the percentage and can all be avoided. Flash Shift, Pulse Radar and Space Jump can be skipped through normal playing, and most major upgrades are skippable with glitches except:
*Morph Ball
*Charge Beam
*Phantom Cloak
*Spider Magnet
*Grapple Beam
However, you cannot skip all upgrades in the same run, as some upgrades are required to skip others.
==References==