MM5 gravity skip

[Forum post from 2015]

Short version: Do a short jump within 18 frames before the fanfare so that you're in the air as it's supposed to start. With a 1-frame tap you'll get grav skip 100%, with 2-4 it's still a very high chance.

The mechanics behind gravity skip:

The gravity in the game depends on memory address 52. If this value is zero, gravity works as normal. If it's nonzero, gravity isn't applied at all and the counter decrements by one each frame. In normal stages it always stays at 0. While underwater or in low gravity area, any time it's 0 it gets set to 2 the next frame. In practice this means that gravity only applies every third frame, or is one third as strong as usual.

While nothing relevant is happening, this counter will keep going 2 1 0 2 1 0 2 1 0. Whenever you press A while on the ground (i.e. jump), the count is inverted for the next frame, so that if you jumped on 2 the next value will be 0 instead of 1, and so on. After that one frame the value will continue cycling as usual. This isn't useful in any way and I'm only mentioning it for the sake of completeness as it seems to be the only way your input can directly affect the counter.

Whenever you get hit, the value freezes for a moment. If it happened to freeze at 0, you'll get normal gravity then. If it froze at 1 or 2, you get no gravity, you'll just slowly float down at the small constant velocity the hit itself puts you at. The same thing happens as the stage end fanfare starts playing and you lose control, so barring any manipulation it's a one in three chance.

The manipulation depends on the interaction of two things:
1) The stage end fanfare works like all cutscene events such as boat in Wave and Proto Man in Gemini, in that it will only start if you're standing or walking on ground. If you're sliding or in the air, it's delayed until you return to neutral state.
2) Because the counter affects gravity, the length of your jumps can vary by 1 or 2 frames depending on its value as you jumped.

Specifically, it turns out that a 1-frame tap of A results in an 18 frames long jump on a frame where the counter is at 0, 19 frames on a 1, and 20 frames on a 2, give or take a bit depending on which frame you count as the ones starting and ending the jump. This means that the value of the counter as you land is always the same, and it also turns out it's 0. Thus if you do a 1-frame tap of A within 18 frames before the fanfare starts, you'll always get grav skip. Do note that this also causes you to lose some frames to delaying the fanfare, the more the later you jumped.

For inputs of other lengths, a 2-frame jump gives you a 2/3 chance of landing on a good frame, 3-frame gives 3/3, 4-frame 2/3, 5-frame 0/3 and 6-frame 0/3. A full jump to the ceiling of the boss room gives 0/3.

edit - I realized later I didn't test different subpixel values for those odds and most of them are probably off. It would be cool if someone could be arsed to get accurate numbers, but regardless of those it's clear that the odds are way better than the random 1/3 chance and that you should be doing this.