0.01 lap by abney317
Forest explaining 0.01 flap strat
2.13 lap TAS
2.75 lap by abney317
22.28 3lap TAS
24.29 3lap by abney317
0.01 YV flap strat
There are 4 different paths on YV that the game tracks. Taking the far right path and then setting your last section to 1 allows this setup to work. You can cross the finish line by getting within 1000 units of the path marker for the path the game thinks you're on. You do this to finish your first lap, then while the kart is over the canyon floor it causes the game to switch which path it thinks you're on, taking you back outside of the 1000 unit sphere. This gives you a 1 frame window to move back over the finish line without subtracting a lap and lets you cross over again to complete another lap. This shortcut can be done on any version of the game with any character.
2.xx YV flap strat
For the 2.xx YV flap strat to work, you must cross the finish line backwards while outside of the 1000 unit sphere that surrounds the center finish line. While outside of this region, the finish line is not active, so it will not subtract a lap. You must then bounce off the wall in a precise way so that you get back inside of the 1000 unit sphere and then cross the finish line forwards.
3lap
The 3lap now involves doing the regular lap skip jumps on the first 2 laps and then going for the 2.xx flap strat to end the race on lap 3 to avoid an extra Lakitu pickup.

Old 3lap WR Strat

3lap videos:
3lap WR video - 27.73
27.66 TAS by Forest
Example of a 9.27-9.23-fail run where I crossed over the fence slightly too far to the right
How does this shortcut work?
You jump over the fence (within a certain distance of the finish line), then cross the finish line backwards while the game thinks you're on the other side of the track (the part of the wall you hit). You will get placed back on the road based on where you crossed over the fence. The game thinks you drove around the entire track and gives you the lap.
How can you save a frame over the 27.76 runs?
By getting placed further forward, it is possible to jump towards the wall with an angle more parallel to it, which keeps more of your momentum as you fall making it possible to save the frame. This has to be balanced with the fact that if you get placed too far forwards for the last lap attempt it can end up being from too far away for the 27.73 to be possible.
Why wasn't 27.73 done earlier?
Most people over the last 10 years that are doing WR attempts on this have shifted towards doing the left of tree lap 1 strategy to get more consistent good placement for lap 3. This makes getting the faster lap 2 time nearly impossible because of the placement on the track. Knowledge of why we're able to do faster laps while being a little further away from the finish line only recently became clear to us with Forest's TAS.
Can 27.70 be done?
The TAS is 27.66 for this strat, but for that time save to be possible we'd need to be able to cut a frame off lap 1 or lap 3 which is a challenge but maybe possible.
What is this ghost you are using for?
If you see me using a Wario ghost for the 3lap shortcut. It's there for a "good placement" marker. I can get placed on the same spot just in front or just behind after the first shortcut. After the 2nd shortcut I need to get placed exactly on top of where it is. After my 3rd shortcut I need to get placed on top of it.

Example of behind ghost after first SC
Example of same spot as ghost after first SC
Example of in front of ghost after first SC
SC 3lap Ranks
SC lap Ranks
SC 3lap WR history
SC lap WR history