I don't know if this has been talked about but whenever I was messing around with Roy in training mode I found you could reverse his aerial momentum by pressing neutral b and then quickly holding in the other direction, I never tested how many frame you had for it but it wasn't to hard to perform
Then when I was using Corrin it turned out they could do the same thing even though their neutral b wasn't completely reversal like Roy's. It turned out while in the air after pressing B there was a 3 frame window to hold in the other direction and reverse your momentum and way Corrin is facing. The neutral b is also reversable on the ground with a larger window that I'm yet to test.
Then when I was using Corrin it turned out they could do the same thing even though their neutral b wasn't completely reversal like Roy's. It turned out while in the air after pressing B there was a 3 frame window to hold in the other direction and reverse your momentum and way Corrin is facing. The neutral b is also reversable on the ground with a larger window that I'm yet to test.