Some brief documentation on the TAS used 2-3 clip. Credits to callumbal for his own documentation (feel free to elaborate further here) and jesusftb for first pulling off the glitch. I may add images to this later on.

SML Out of Bounds glitch: 2-3 skip

What it is: It's a glitch that allows you to wrap around the screen in Super Mario Land. In 2-3 a very specific setup is needed to get past the barrier for the stage exit to save around 3 seconds.

3rd pillar, last block on the end above the 1 unit gap.

Set yourself up so that you're in line with or slightly below the block

At the middle gap of the sub press down+left for a small window and shoot the block in front of you after you're wrapped around.

When the clock goes to 268 alternate between down and left quickly. You should then hit the goal.

What can go wrong:

Incomplete wrap: you don't wrap around the screen fully before the block is broken, a second timeloss, failed trick.

Shot wrap: Shot gets screenwrapped, failed trick.

Too early, hold left for too long: hit the seahorse, lose mushroom, failed trick.

Different location: can appear above the breakable blocks and goal switch, slight time loss.

Too late: can appear behind goal, failed trick, minutes of timeloss.

Nonexistent coins can be collected offscreen.

stickying this and adding my own video tutorial for completeness: https://www.speedrun.com/sml1/guide/x1fhh