How exactly does the immediate turn around from wavelanding work?
There's 3 options for wavelanding on a platform and escaping it facing at the opposite direction:
1) Waveland on the platform at a spacing and angle such that you will fall off precisely on frame 12, counting the airdodge input as frame 1. In the window of frames 9-11 input smash turn (the type of turn you input during dash dance, which requires a smash input) so that you turn on frame 11 and then fall off facing the new direction. As far as I can tell, this is what @
Renth
did in the video he linked. Can't be sure because of video quality though.
2) Waveland on the platform a bit further away from the edge, so that it will take 19 frames or more to fall off, but so that your waveland can still carry you off the platform. Immediately after wavelanding start holding the control stick in the opposite direction, so that you will tilt turn starting on frame 11. Then on frame 18 your turning animation finishes, and you will face the opposite direction you were sliding to if you fall off on frame 19 or after. If you fall off before the turn finishes, you will remain in the original orientation.
3) Waveland into turn moonwalk: This is by far the most lenient method, and I think it's also most practical, since you don't have to fall off the edge on a specific frame and don't have to turn precisely. However it might be a bit easier to react to and a little slower, since the dash negates a bit of your airdodge momentum.