It's humanly impossible but here it is. Quoted from Kadano's guide.
Here is an animation of frame perfect ledgedashstalls (repeated use of 287°-295° airdodges):
Frame-by-frame rundown:
1-8¹ (ledge grabbing animation) you can’t let go of the ledge.
9 press down or away. To get the timing right, I recommend reacting to the ledgegrab animation or sound effect as 8 frames are pretty much exactly as long as good human reaction times.
10² jump and hold towards the stage.
11-24 hold towards the stage.
25 waveland backwards with ~290° (SSE if you think of the control stick as a compass)
30-35: Fastfall on any of these frames.
¹Sometimes, letting go is possible on frame 8, but this happens rarely and I don’t know why.
²You can delay the jump for 4 frames if you don’t fastfall before the jump. Doing so requires you to fastfall earlier after wavelanding. The fastfall timing windows overlap at two frames, 5 and 6 after wavelanding.
You must let go of the ledge on the first possible frame, though—else you are vulnerable at the end for at least as many frames as you delayed it.
The hardest part is probably getting the correct angle on frame 25. If you prefer doing a 315° angle (SE), you can use a slightly different algorithm that also has full invincibility:
1-8 (ledge grabbing animation) you can’t let go of the ledge.
9 press down. To get the timing right, I recommend reacting to the ledgegrab animation or sound effect as 8 frames are pretty much exactly as long as good human reaction times.
10 hold down.
11 jump and hold towards the stage.
12-27 hold towards the stage.
28 waveland backwards with exactly 315° (SE, easy to do because of the octagon carving)
31-34: Fastfall on any of these frames.
