WORLD RECORD RECORDING
12% is the lowest amount of items in which a human can beat the game via defeating all major bosses while using out of bounds. It is perhaps the most difficult humanly possible category to optimize, and has only been completed in a single sitting by sniqwc3.
For humans, the items that make up 12% are the following:
Power Bombs are required to open orange doors and destroy other destructible surfaces that block the way. They are also required to kill Metroids as Ice Beam is skipped.
Charge Beam is required to defeat bosses, as otherwise, an extremely high percentage of ammo would be required instead, which would defeat the purpose of this low% category.
Varia Suit is required as otherwise, Mother Brain's Rainbow Beam would deal 600 damage instead of 300 damage, as it only checks for Varia Suit - not Gravity Suit. Varia Suit would otherwise require three additional Energy Tanks in its place, which would defeat the purpose of this low% category.
Related to the above, three Energy Tanks are required to survive Mother Brain's Rainbow Beam.
One Missile expansion and three Super Missile expansions are required to open appropriate doors and cause Mother Brain to change from her first phase to her second phase. The first Missile pack in the game is required to 'awaken' the planet, same as Morphing Ball. You can alternatively acquire a second Missile expansion instead of a third Super Missile expansion depending on your route.
X-Ray Scope is required as it not only allows the Zebetites to be skipped while still allowing access to Mother Brain (same as Ice Beam and Speed Booster), but allows "X-Ray climbing" to be performed to travel through rooms by utilizing their out of bounds areas, which is the primary exploit of the run.
TAS can use the following item set instead:
Speed Booster is a second means of entering the out of bounds, as depending on when one pauses during a shinespark, they can pass through door transitions. TAS would not need Speed Booster for such a thing as it would only require it for escaping Draygon's entry chamber and skipping Zebetites; however, using a shinespark to pass through a horizontal door transition would be much faster than without, as passing through a horizontal door transition without Speed Booster would require multiple pauses and frame-perfect movement inputs as opposed to a single pause and a frame-perfect/position-perfect timing of the shinespark.
This branch of 12% is considered TAS-only because the only known way to reach the Maridian mountain with these items and a retained blue suit is by entering it from the Red Brinstar connecting area, which involves entering the Red Brinstar elevator room's out of bounds area. Normally this would not be an issue for humans as you can enter the out of bounds by shinesparking through the upper left door, but because you need to keep the aforementioned blue suit retained before entering Maridia, shinesparking is not an option. Additionally, it is not humanly possible to climb up the room before the Colosseum while retaining blue suit, nor is it humanly possible to travel back through the Colosseum once Draygon's entry chamber is escaped. Essentially, it is currently impossible for humans to reach Aqueduct while retaining blue suit with these items.
For better understanding of this branch, sniqwc3 has recorded a tool-assisted playthrough.
Tool Assisted (Theoretical)
Theoretically, TAS can also use the following item set:
TAS can trigger Mother Brain to enter her second phase while stuck in the right wall via Rinka freezing (making Ice Beam necessary), then X-Ray climb up into the ceiling and fight Mother Brain's second phase from the ceiling. Wave Beam is required as it, and only it, allows charged shots to pass through the ceiling and strike Mother Brain.
Before rainbow beam is fired (which can strike the player no matter where they are in the out of bounds and drag them immediately back into the room), TAS would have to reach the proper position in the out of bounds to create the Varia Suit and then acquire the Varia Suit, which is only possible by being touched with the Grapple Beam, else the game crashes.
Acquiring the Varia Suit immediately places Samus back in the middle of Mother Brain's chamber, and allows the game to be paused during rainbow beam, which allows pause abuse to be used (thus no Energy Tanks are needed!) until the Super Metroid refills Samus's energy. Then everything can finish like normally.
sniq - Shows how to complete 12% using the KRDP route with a hitbox viewer present. Not necessarily a tutorial, but is currently the best resource for learning the category.