ZD vs WaDi:
Fox vs ROB:
So, Fox/ROB isn't awwwfuuullll, at least not Sheik/ROB bad. But ZD has upgraded his playing a bit. Compared to say, Xanadu 200, he doesn't rely on roll to either reset neutral or get out of a situation, but instead used Fox's excellent ground mobility. His spacing was on point, and he was catching a lot of WaDi double jumping to escape to land. ROB doesn't have the aerial mobility to spare to liberally use an approach to Fox, even if it is for a Gyro set up or laser pressure.
ZD was also far more comfortable playing up close than he has been, keeping the space between him and WaDi to a minimum, and using Fox's superior mobility and buttons to pressure WaDi into some bad decisions. WaDi's anticipation/reaction skill seemed to be affected by ZD's strong rushdown game, and he missed quite a few opportunities to either ledge guard or punish that he would normally hit.
ZD clearly has been grinding out the ROB MU and played it rather confidently.
Mewtwo vs Fox
The Mewtwo side of the coin was a bit closer. WaDi cut down panic airdodging and played how he normally does with a few minor exceptions. He seemed to want to re-establish some degree of psychology dominance in Grands and went for some ill-advised hard punishes - like a randy Fsmash and a deep ledge guard that he initiated before ZD even attempted Fox Illusion.
In addition, throughout all the sets, ZD had a reliance on FH-Dair to approach that WaDi never really took advantage of. Other than Uair, Mewtwo loves trading Fair with Fox's aerials. One of these days, WaDi will take a page out of Rich Brown's book and start to C-bounce Shadowball on the ground to bait out buttons.
FWIW, I don't think Fox is that awful for Mewtwo. Mewtwo players have a tendency to over-rely on their airdodge in most MUs (because they can). Unfortunately, once you establish a habit like that, it's hard to break in the MUs that you can get bodied for it.
Fox enjoys eating airdodges almost as much as Wario likes eating his bike.
Wii Fit Trainer vs Fox
WaDi's Wii Fit is actually pretty decent. I just think unless you live in Foxville like John Numbers, you may have a bad time with the MU.