I think I did a write-up on this a while back. Oh well....
-CC Fairs to a shield or dash away I guess and the first hit of Nair to shield
-when Marth is Fair walling, it helps to do FH Nairs that end just as you hit the ground so that you get the hang time from using a Nair and you reach over Marth and hit him as he lands.
-Marth tends to DD away to pivot grab vs Fox. To compensate, Fox must aim his Nairs behind where Marth actually is in order to hit. Problem is, Marth can go under Fox or shield(and possibly grab) to punish Fox when he does this. Fox then has to mix in straight dash in JC grabs. It's a big adaptation game and whoever baits better in this situation without losing control tends to win.
-Uthrow Uair as much as possible. Once Marth can't be Uair'd, try for Bairs so you can force him offstage(he'll probably be drifting off anyway but make it worse for him).
-Don't challenge Marth offstage otherwise(unless you hang onto the edge to shine Bair so you either shine spike him or Bair his delayed recovery while invincible).
