Wait, didn't I find this a year and a half ago?
Just looked.
"8: Initial Dash De-Sync. Jam the control stick in the direction opposite to where you're facing, let go, and towards the end of the dash, input Blizzard, Ice Block, or Shield + any move. Only Nana responds at first, so she Blizzards, Ice Blocks, or Shields alone, leaving Popo to do anything. The timing on this is tricky, but in my opinion worth learning.
Credit: Discovered by me on 02-16-2008. I tested this in Melee and found out that this was possible, but harder to do and less useful because Ice Block came out slower."
Hmm well. For mine you don't need to dash the opposite direction, you can keep running, you can grounded b-reversal and you can't really input it through a buffered dash you have to keep going a little I think.
Very similar though and it could be the same thing though absolutely no one uses it, especially my b-reversal method :/.