omg
the fox boards cultivate a brand of *********** that you just can't find anywhere else on smashboards
That said, I think I finally figured out what causes up-B's to turn around when you're facing one direction, and you go straight up.
There was a thread awhile back (I think Axe posted it or something) which detailed the turnaround frames different characters had on their up-Bs. People were like, "I've done this with fox, how does it happen?" or "How can i do it consistently?"
I noticed that it usually happens to me when I miss shine-upB stalls.
Anyways, here's the rub (at least as far as I can tell with the amount of testing I've done):
If you up B between like 1/4 and 3/4 of the distance that firefox travels when it's going straight up, and if you're passing the edge on a stage (battlefield, dreamland, fountain, and yoshi's all work I think), and if you're hugging the stage, you'll go straight up facing one way, then turn around the other way, and go into fall animation facing the opposite way you started.
So, for example:
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if that's your vertical firefox, and the edge is somewhere between those 2 dashes when you pass it, you'll probably turn around. You also need to be close to the edge when you pass it, like within grab-range.
!!!
This is really interesting to me, because it's something that bugged me when it happened, and it's something that I've wondered about otherwise. Test it on your own; I think this is the way it goes. Maybe it has to do with the little flip that Fox does when he starts (or is like midway thru) his up B, some shenanigans happen when he passes the edge in grab range. (My theory at least)
So test this **** out, I'm pretty sure this is the way it goes.