It's mostly just muscle memory on the harder parts like the jump through the goombas in 1-2. The game is very in depth considering it's only 5 minutes long. All the movement in 4-2 is intentional to make the screen scroll to the right, meaning Mario can go down the pipe and appear in the vine warp zone without watching the climbing cutscene, for example.
If this run interests you, I'd recommend learning about some of the things done in the current record. It really is incredible how far the game has been pushed.
I would love to learn the specifics of how it's done. Do you have any videos that break it down?
I like how the player didn't use any of the wall glitches in the run.
I like how the player didn't use any of the wall glitches in the run.
I am the player. I think you might be referring to the wall jump off the pipe in 8-4, or perhaps the wall clip in 4-2. I don't do either of those because they are inconsistent and do not save that much time, I can beat my time without doing them.
Here is a video explaining all the intricacies of the speedrun. It references the old record, which is only about 0.2 seconds slower than the current one.
I can't imagine being this awesome at Mario.
I am bad. Like really bad. This blows my mind.