Half A Presses and ABC

What is a Half A Press?

Teal Deer; Hold the A button.
Essentially, a single A Press is exactly what it sounds like: a single A Press. A single A Press will add one A Press to your run, or your IL, or whatever you're doing. A Half A Press is when something adds or removes an A Press outside of your current context. For example, suppose you were doing an IL, and the level required you to hold the A button. In that case, you can hold the A button before you start the level, and then you can complete the level without adding any additional A Presses to your run. It still requires you to press the A button at some point, but it doesn't add any additional A Presses.
Here is an example of that.
https://www.youtube.com/watch?v=kpk2tdsPh0A
Another more complex example would be leaving a level in a way that removes an A Press outside of the level. This would be a Negative Half A Press.
Here is an example of that.
www.youtube.com/watch?v=5pmjLkuhwY0

What is ABC?

Teal Deer; Don't press A.
ABC is short for A-Button Challenge, and it's attempting to beat a level or game in as few A Presses as possible. It originates from Super Mario 64. Nearly all of pannenkoek2012's videos are dedicated to ABC. Currently Super Mario 64 requires 1 A Press to beat Any%. Super Metroid, AFAIK, requires 0.5 A Presses to beat Any%. Now unlike Super Mario 64, 0.5x in Super Metroid should be humanly possible and I don't see any reason why it wouldn't be.

How do you jump?

Teal Deer; Turn around.
By pressing back during the turnaround animation, you do what is known as an "auto-spinjump." Auto-spinjumps add no additional A Presses, but require an initial A Press, which is done before powering on the console (or resetting). While they are useful, alone they are not enough to beat the game 0.5x. Auto-spinjumps have two major limitations:
A: They kill your horizontal speed, severely limiting your horizontal distance
and B: They have a fixed vertical distance that cannot be extended via wall jumps or cut short via letting go of the A button.
However, we do have ibj, which has limitless vertical and horizontal distance at the cost of being slow. We can also shine in certain circumstances to cross large gaps and/or gain large amounts of vertical height. Both of those (should be) enough to get us down to a single Half A Press.

What about 0 A Presses? Is that possible?

Teal Deer; No.
After getting bombs you might possibly be able to make your way through the rest of the game 0x, but it would suck. A lot. I'm actually no where near certain that you could do it because you aren't able to shine which may prove necessary at some point, and I'm also not sure if ibj is fast enough to not die in Amphitheater. You can probably make it if you have nearly every E-Tank in the game, but luckily for those of us playing the game, we can't make it to bombs 0x because before we can get Bombs and/or Speed, we need auto-spinjumps to get through Ceres, Pit Room, getting Morphball, traveling to and getting out of Construction Zone, getting out of Brinstar, going back through Pit Room, the Climb, Parlor, and Flyway. I'd rough guess the minimum number of A Presses to be around 40ish, mostly depending on how many A Presses are required for the Climb and Parlor. That estimate is very crude, but overall is conservative and the true amount is likely higher. Until all of those A Presses are eliminated (which will never happen until ACE &/or some form of zombie hovering gets found in Ceres 1 or 2), we don't need to consider ibjing the entire game.