Try to dissect what you are doing into individual actions at first. In this case, you're going to be jumping towards stage side > pressing opposite direction on control stick to wallhop > pressing B > quickly reversing direction > wallhopping again. Go into training or start a timeless match on YS or GHZ and try and go through the motions. If you don't get it at first, just keep working at it. Don't get aggravated; that will slow you down a lot. If you do, just start from square one and try to dissect again. Start being able to do one B-reversal wallhop off of wallhop; when you start getting consistent you can try and do two consecutively, three consecutively, etc.
TL;DR - split it up into individual button presses, and try and speed up the process as you go along. And, sorry, but PRACTICE!
