Oh I'm about to change your life.
Hold attack. I have L set to attack so this is easy. If you don't have an easy way, you can claw, but that reduces how easily you can do this in game.
So you're holding attack. Say you want to moonwalk to the left, so you're facing right. Do a normal moonwalk right>left, still holding attack, then at the end of the 'dash' just hit the C-Stick to the right. Repeat at the end of each dash.
There are two other C-stick tricks that I know of similar to this. If you hold attack and walk in a direction, then hit diagonal up + behind you on the C-Stick, you'll do a pivot but keep moving in the original direction. It looks hilarious.
And then you hold attack, do a full run, and to quickly run in the other direction, flick down on the C-stick and immediately hit the other direction on your control stick. This causes you to crouch for a split second, then dash out of the crouch. Essentially a dash dance that isn't limited by distance.
For the last one, sometimes you'll moonwalk instead of change direction. I'm pretty sure this means you're hitting the other direction while still holding down on the C-Stick. Running right and immediately moonwalking back to the left looks pretty jokes.
Since these all require you to be holding attack, their use in a game are limited because you have to either jab or figure out how to press A without triggering an action, i.e. on respawn or during endlag.
Now here's something funny. 3.5 registers different buttons as different inputs. So you could actually set R/L to attack and hold it down the whole game, without affecting your A button.
This is the new meta. I'm heralding this in.