Really_Tall | Paper Mario: TTYD - Don Pianta TAS Timesaver @Really_Tall | Uploaded 8 years ago | Updated 2 hours ago
This was already possible on US/PAL using a Flurrie Superslide, but this method works on JP as well. This can be done after both times you talk to Don Pianta, which saves time from movement and also skips an email, saving around 10 seconds overall.

To do this, first jump towards the door. Keep holding down, then on the first frame of landing press R, A, START (or a direction on the dpad), and right on the stick. Unpause and you should walk to the right while in paper mode as the door opens, like in the video.
The ! mark has to appear right before you pause for this to work: you may have to hold slightly down from right to make it appear.

This high quality video was made possible thanks to @Rainchus (Hi Rain!!1!1), who has bugged me to dump frames since forever.