You wanted to know how to moonwalk with marth and Roy, sry I've been absent on swf for quite a while so here's the reply (don't know if still needed....sry for being this late oO)
Moonwalking is pretty much the same with every character, the timing is a little bit different, but the basics are identical.
you press the stick in the direction you want to monnwalk to and go in that direction.
then you quickly do the folloing movements:
press the stick in the opposite direction then do half a circle to the other sde by pressing down.
moonwalk example to the right side:
walk to the right.
press left, down left, down, down right, right.
with a little bit of practice it is not that hard to do and looks pretty cool.
i hope the instructions are useful otherwise send me a PM and I'll anser as good as I can^^