On the contrary, I was absolutely destroyed by a WFt today. It's actually not a bad matchup for her/him.
If Mario's throwing a lot of fireballs, the football and Sun Salutation seem to work well.
As for the grabs, I find WFt's dodging very confusing, and spot dodges can really throw a grab off. If he grabs a lot, spot dodge then DSmash him a couple of times to rack up that damage, or mix in a few grabs and throws of your own.
Mario's Nair seems to have a pretty high priority. For that I'd recommend that if he Nair's as soon as he approaches you, just air dodge and follow up with another aerial. Again, mix up the timing of your dodges or use a surprise aerial to knock him off guard.
Hope this helps you out
Now hold that posture!
Edit: Also, 100th post! Woot!