Early Sasa Sanctuary
This allows you to skip the Satomi Power Orb quest and get Waterspout quickly. You can also fight Gi (aka Take) before getting the Canine Tracker. This makes the game think you've already fed one of the four dogs in Kusa Village, causing the fight with Tei to trigger after feeding only three dogs. If you avoid feeding Ko (the dog in the long cave that normally requires Vine to reach), you can feed her next to Fuse after the Tei fight, which warps Ammy into the cave, saving some time when leaving Kusa. This currently isn't used in any category, though, because NG+ Any% skips feeding the dogs entirely, and NG+ AB skips fighting Take (see https://youtu.be/GNUdUScSanU).
Right after entering the area, go right and jump up next to the rock. Do one KT up, using your second wall jump to go right towards the loading zone. Do one more KT to clear the loading zone and run up to the edge of the area.
Jump off, hold the map button and start aiming towards the origin mirror. When the background changes colour to a lighter blue, hold the direction for two more seconds, then let go. You should land directly in the main hall.
You can also land in the hallway towards the hot springs, but this is a bit more risky and should be avoided by newer runners.
If you land in the Sparrow Boss' room, simply jump down the elevator shaft. Make sure you don't land on top of the elevator, because this will soft lock the game.
It is possible to perform an interior clip into Sasa in NG (see https://youtu.be/muYd3YXUDXU). Unfortunately, this is currently only known to be possible with double jump. Since Waterspout is a prerequisite for double jump, this is not useful.
If this were possible without double-jump, it could be used to obtain Waterspout immediately after Blooming Taka, allowing you to delay visiting Kusa. The entire Canine Warrior quest would still be necessary to complete, however, as there is no known NG method to access Gale Shrine early.