Sherm Skip finding, described by Syrkl.

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Cappy Return Cancelling discovery
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Cappy Warping (Glitch): In 2p if you press X/Y/A/B on Cappy's controller the frame before the cutscene of warping to any Checkpoint
     flag ends, Cappy will spawn at the Odyssey and fly to Mario's location instead of appearing above Mario's head like usual.
     Important to note: If Cappy doesn't make it to Mario's head for 3seconds, the game considers Cappy stuck and instantly teleport
     him to Mario's head.
Discoverer of Cappy Warping: JKB
When?: Almost 2 years ago?
	 While JKB and I were trying to get Bruncheon Jump in 2player (before it was known to be possible 1player) JKB found that by
     spamming A on Cappy's controller whilst warping to Luncheon painting Island, Cappy seemed to sometimes spawn by the Odyssey for a
     few seconds before appearing on top of Mario's head.
When?: 11 January 2018
     Video: https://twitter.com/JKBSunshine/status/951312138676482048

Cappy Clipping (Glitch): By standing close to a wall in 2player and crouching with Mario, then shaking the Cappy controller, Cappy can
     clip through the wall. (This is essentially the same thing that is happening in CRC but there isn't really any warping as it is
     done at point blank against a wall. Warping Cappy around without a checkpoint still hasn't been discovered around at this point)
Discoverer of Cappy Clipping: Shaeden & Ikkitrix.
When?: Around 2 years ago?
     Noguy5 had posted on the discord that Shaeden and Ikkitrix had found a way to clip Cappy through walls in 2Player.

Cappy Return Cancel (Glitch): Being interested in the Cappy Clipping glitch myself, I wanted to know how it works exactly, after a lot
     of testing I found that you are essentially overriding the animation of Mario putting Cappy back on his head by Crouching. By
     pressing Y on the frame before Cappy appears on Mario's head; Cappy will teleport, doing this at point blank allows clipping the
     wall directly infront of you, but I then experimented doing this but whilst Cappy and Mario had distance between themselves. This
     was when I found Cappy Return Cancel (originally I called it Cappy Teleporting), done by waiting for Cappy's 3 second (about 1sec
     if he is against a wall) Return timer and hitting a flight button (Y/X) 1 frame prior to Cappy appearing back ontop of Mario's
     head.
Discoverer of Cappy Return Cancel: Syrkl
When?: 22 April 2018
     Video: https://twitter.com/kehzou/status/987865455313350657

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How Sherm Skip was discovered
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On Feb 19 2020, I was trying to get a glitch that would allow Mario's vertical speed to be locked during his painting animation to hopefully get enough height to simply jump over the void and make the Metro painting building to Mainland jump.
Since this wasn't working well, I decided to think back to my findings on the Cappy Return Cancelling glitch (also known as CRC) years prior. I thought of attempting to use both the Cappy Warping glitch and CRC together to get Cappy to spawn near the odyssey and to remain there permanently. If I could do this then I could perform another CRC but aim Cappy's analog towards the Mainland checkpoint and hopefully warp Cappy ontop of the checkpoint, similar to what is happening in my Cappy Teleporting video but with much more distance... However, I also had a theory that Cappy's resulting distance would not be long enough due to his ending warp position still having the same distance between him and Mario in the direction you warp to. (When plotted on a graph this is a circle, so jokingly it was called Syrkl Theory)
Even though I didn't expect it to work, I posted a clip of Cappy being stuck on the railing by the Odyssey after I performed both a successful Cappy Warp glitch, and then Cappy Return Cancel.
Here is the clip posted Feb 19 2020 https://twitter.com/syrkl_dsc/status/1230247861113090048

A few moments later, Icay was interested in testing for himself so I taught him how to do the inputs to get Cappy stuck up by the Odyssey. Icay then found a better way of getting Cappy to warp in the direction you wanted precisely, he found that instead of using the analog on Cappy's controller like I was doing, you can just use 0 analog input and Cappy will warp in the direction Mario is facing. This was very useful because aiming the analog was very inconsistent. Icay posted his results, but still the distance wasn't great enough to make it to the Checkpoint. https://twitter.com/Icay__2/status/1230280257816518656

Although many people (Icay, GRA, Grady, Relaxmas,  Littlerootlodge(Lloyd), Warspy, & Luigi's hat to name a few) tried different strategies such as jumping to the Northeast off of the Redcrate to increase the size of the circle, or doing a backflip to ensure Cappy can warp above the Railing near the checkpoint, it still seemed that it was impossible from this position due to Cappy not having enough distance at his current location (being trapped by the railing near the odyssey).

The next idea was to increase the Circle more by trying to get Cappy stuck on the west side of the building by the odyssey, this should hopefully give enough distance between Mario and Cappy that; post CRC warp, Cappy will hit the checkpoint. Here is a diagram of the circle size: https://twitter.com/kehzou/status/1231231157146136576 as you see, it should definitely hit the checkpoint if our calculation is correct but there was one problem, we had no way to get Cappy stuck on the west side of the odyssey building yet.

Nothing seemed to work until later Russell had the idea of using a slope to change Cappys vertical warp position (also known as an SCRC), although not useful for sherm skip, this is VERY useful for future bowsers checkpoint warps because now we can change the position of all Cappys 3 dimensional positions post warp. And then; soon after, the final piece of Cappy Return Cancelling tech was found, Lloyd made a joke by saying something along the lines of "if you GP down cappy when your sloped, it might turn height into distance". I tried his outlandish idea... and it worked. Now, not only could we control the exact coordinates Cappy can warp to, but we could also control the distance as long as there is a slope nearby Mario's standing position. (It is important to note that at this point; after it was discovered that we can transform Cappy's vertical distance into horizontal distance (also known as a ZCRC), we already theorized 3 caps would be possible since we thought this would be possible in Bowser's kingdom.)

We all immediately try the West Side of building theory. Only I and Lloyd (later Grady too) have successful attempts due to how hard the timing of the glitch is. But unfortunately it seems Cappy still is a tad too short to hit the Checkpoint.

Soon later, Qflame, used an emulator and memory editing tools to try and force Cappy to hit the checkpoint from the position we were using after a CRC. He successfully got it to work by editing Cappy's coordinates and throwing him really far out past the West side location, thus ensuring that Cappy had enough distance post Warp. The reason I didn't think this would work is because I thought Cappy would only warp successfully if Cappy was stuck on a wall somewhere, such as the west side wall we were trying. But this was actually just a slight misunderstanding of the glitches mechanics.

After proving that Cappy can indeed hit the CP, Qflame went on to predict, that to get the distance he had, you would need to groundpound for upwards of 10minutes. Because of this, many people were demotivated, doing 10minutes of pressing ZL/ZR then having to time a 2-frame window twice was just too much.

Later that night I couldn't sleep and had another theory to not only get Sherm Skip without hacking, but to also do it in much shorter than 10minutes of time. This was what I posted to the discord, just so I didn't forget the next day:

"My method for getting Sherm skip would be
-position mario on slope by railing
-GP with cappy into void for 3min
-perfect CRC 1 using pause buffering to time the Y press
-cappy now has negative height converted to distance
-move mario ontop of crate, duck and aim directly towards the checkpoint, meanwhile periodically groundpound with cappy to save distance
-shake like mad until cappy hits checkpoint
I guess you could do like 4 min or 5 min GPs but i dont think its necessary, coordinating climbing the box and Gping shouldnt be too hard, just GP inbetween specific movements, using pause buffering to switch controllers, only need to press GP on cappy controller once every 2 seconds"

My idea of stalling Cappy's distance from Mario by groundpounding was one of my better ideas as now you only need to groundpound for little time rather than 10minutes as previously predicted.

The next morning, I tried this method. First I made an audio cue so that; instead of pause buffering, I could just time the button presses instead. Then I got to grinding it out.

It only took around 1 hour, and my method worked, this is the result: https://twitter.com/kehzou/status/1231545393722187776

Quick note to end on is that the backflip with mario in the Sherm Skip video is completely unnecessary. Cappy makes it fine past the railing and hits the CP with no worries. I did the backflip just as a precaution, but thought it was necessary until further testing.