This shortcut was discovered by Forest64 with numerous adaptations from the community that shortly followed.

Forest's original 150cc proof of concept
Forest's proof of concept for current 3lap time trial opener strat
0.01 flap by abney317
14.24 3lap TAS by Forest
21.57 3lap by iMath
How does this work?
The 3lap WR strategy for JP 1.0 works because Lakitu places you back on the track where you last were instead of where you landed like in the later releases.
By jumping off the track from a specific spot we can trigger a section jump change that gets stored. The grass on Toad's Turnpike is not properly mapped to a section, allowing us to abuse the last section value that we stored. If we go backwards over the finish line and get stuck out of bounds at the same time we can skip a full lap due to the game thinking we are far enough away from the finish line for it to not subtract a lap from us.
The lap uses a similar strategy but also relies on avoiding getting stuck out of bounds. It's the same concept but you can actually just clip the wall to do the lap skip instead of getting stuck. VAJ does this accidentally on one of the laps in his 25.33 run, and iMathII does this on purpose in his 24.46 run.
Why are you not using Bowser like a bunch of the other 3lap runs (if I'm not using Bowser)?
Makes almost no difference. I'm mostly just testing, but in theory lightweights should actually be very slightly faster.
Why are you using Bowser (if I happen to actually be using Bowser instead of Toad)?
Going for a wall clip on lap 3 tends to be a bit easier to pull off with Bowser. For the fastest strats there are specific setups that require Bowser.
How much time does this save over the "original" shortcut?
About 1 minute and 5 seconds for the 3lap. 28 seconds for the lap.
Why do some people go left and some go right when trying to get stuck on laps 2 and 3?
Left seemed potentially easier at the time, but it's not really. Getting stuck on the right side is faster.
SC 3lap Ranks
SC lap Ranks
SC 3lap WR history
SC lap WR history