Toad Town Sushie Glitch

This is a truly legendary glitch in the Paper Mario community. It was done exactly once on console, without video, many years ago... and then nobody was ever able to replicate it again. And not for lack of trying, either.
Well, with careful study of the game's code (thanks decomp!) plus some experimentation, I finally understand the conditions that allow it to happen. Take a look at this diagram of the dock:
i.imgur.com/To...
To understand what's going on and what these lines mean, I need to explain how the process for mounting Sushie when you press c-down works.
1. The game casts a ray from Mario, in the direction he's facing. If there is a wall within 26 units of him in that direction, then we are allowed proceed to the next step, otherwise you can't get on Sushie.
Note that even though it looks like Mario can only face left or right, internally he has a full 360-degree angle. This angle is only set when moving in a direction on the ground. Also, to be clear, the edges of the dock are walls.
In the diagram, the brown line is 26 units away from the bottom-left dock edge. This means that the area below the brown line shows the area where mounting Sushie is possible (at least when Mario is facing perfectly diagonal down-left).
2. The game decides which of the edges of the dock you are using. Surprisingly, this has no relation to the wall detected in Step 1. Instead, a ray is cast from the center of the dock towards Mario, and this way continues until it hits a wall. Whichever wall is hit will be the side of the dock that you use. (If a non-dock wall is hit, you don't get on Sushie.)
In the diagram, x marks the center of the dock. Which means the area above the green line shows the area where (if Mario is standing there) the ray will hit the top-left side of the dock in this step.
3. Sushie is placed in the water. She is placed 40 units away from Mario - at a diagonal up-left angle if we hit the top-left side of the dock in step 2, and at a diagonal down-left angle if we hit the bottom-left side.
Actually, even though she's placed 40 units away, she will clip into the dock if she's placed within 9 units of its edge.
In the diagram, the purple line is 40-9=31 units away from the top-left edge. Which means, if Mario is to the right of the purple line and mounts Sushie using that edge, then she will clip into the dock.
So now we can put everything together and consider what happens if we press c-down in the tiny little triangle in the diagram, where the lines nearly intersect. (Enlarged: i.imgur.com/T4... )
First, the game does the initial check that there is a wall within 26 units of us in our facing direction. We are facing down-left, and are below the brown line, so we detect the bottom-left dock wall and this step passes.
Second, the game casts a ray from the center of the dock in the direction of Mario. This ray hits a wall that is a dock edge (the top-left one), and so we will be getting on Sushie via the top-left wall.
Third, the game places Sushie diagonally up-left from Mario. We are so far away from the edge (i.e., to the right of the purple line) that she ends up clipped into the dock instead, and we have Sushie glitch!
Now that we've finally figured out the conditions, it's not surprising that this glitch evaded the community for so long. The precise position is bad enough, but if that was all, I'm sure someone wandering on the dock and mashing would have gotten it again eventually. But Mario's secret internal angle ALSO mattering (which we didn't know about back then, and wouldn't have guessed was relevant now), makes it way too unlikely to luck into again. Only reading modern documentation and testing to work out the EXACT steps Sushie follows was enough to get it done.
As for actually doing the glitch in practice, here are the steps I use:
Step 1: Set Mario's internal angle to down-left, by making sure the last direction you moved on the ground was in that direction. An easy way to do this is by jumping while your stick is in the diagonal position.
Step 2: Using only midair motion, line Mario up against the wall in this position: i.imgur.com/FW...
Step 3: Move Mario perfectly to the left, again only moving during jumps, until you get here: i.imgur.com/tY...
Then press c-down to get on Sushie. Note that it's safe to press it if you're still too far right, nothing will happen. If you get on sushie but don't clip, you're off in a different direction.
Step 4: Explore! This glitch is more famous for its irreproducibility than for its usefulness, but still: Along with stealing the Odd Key and Toy Train as I do in this video, it's also possible to explore:
All of prologue
Chapter 1 up to the Koopa Bros. Fortress door (even if the bridges are out): • Ch1 sushie bridge and ...
Chapter 3 up to Tubba's Castle door: • Paper Mario (rando) - ...

[@Abyssoft]

I love when playground rumor-esque claims turn out to be true.

[@MrCheeze]

One small update, apparently you can change your internal angle without moving, by spinning and then hammering while holding down-left. So it's possible to set up the position first and then change your angle, instead of getting the angle first and position second as I do in the video and description. Thanks r0bd0g for this info.

[@Savestate]

this is badass. love nothing more than closing a long overdue chapter

[@canadianstickdeath]

I refuse to believe this is a real glitch.

[@lior_haddad]

Now I'm surprised someone did it at all! Feels like something you wouldn't find by accident...

[@VeritasUnae]

What a find!

[@Akiironzo]

very cool

[@csolisr]

I wonder if it'll help with at least the 100% record

[@MrCheeze]

probably not