Use Mario against Fox maybe? Not sure how well that MU goes lol.
I personally think it's 6-4 Fox. Both characters can easily rack up damage on each other, but Fox puts Mario in a worse spot than vice versa with utilts. See, as Mario falls he can either air dodge, which I can punish the landing lag off of, or attack, which I can just shield and punish. Rarely a Mario will double jump away, and that gives me the advantage since if I catch him with fair or hair to keep him airborne, he's out a jump and can only hope to catch me with an aerial on the way down, leading back to the earlier situation.
Mario can rack up damage early, but past 50% he's limited to uair juggling to an up-B. He has kill moves but can't set up to them, only try to land them with reads. That's also why I think Luigi is superior, as he actually can confirm into a kill.
But what do I know, I have yet to read up on anything about Fox beyond how his attacks work lol. A lot of my shit is just based on capitalizing off typical player habits and trying to pressure players into taking weaker options, I need to hit the boards.