1. make sure your not getting comboed in your sheild. If you shield and hes behind you when he lands with his d-air, just roll.
2. make sure you block his "combos". A lot of the time you can block the Up tilt after the D air, he has to time everything perfectly for it to be unblockable. The trick for you is that you cant just hold sheild you have to press it as soon as it's available. It takes practice but once you get it down you remove about 50% of his combo potential. This works for every d air combo, if you can time your sheild you can block his next attack, unless he spaced perfectly and timed everthing (including his fast fall) perfectly.
3.ignoring the D air for a moment, he cant combo you. You beat him EVERYWHERE. If you just got thrown and hes chasing you, throw an attack. In the air you have more prioity, range, and speed. He can't beat you with ANYTHING. The only option he has is to force you to attack and then punish afterwards.
4. Make sure he really is attacking. Fox can't beat you anywhere, the only time you have enough lag that he can actually mount an attack is when your in lag from another move. So try defensive stuff instead of trying to counter attack him. Dont fall for the bait all the time.
5.Spam B, fox doesnt have a very good option for stopping the nado, use it, ALOT
6.play on battlefield, or anywhere with platforms.
7.Make sure you save your kill moves for killing.
8.Dont be afraid to get sheild grabed. He can't do jack with his grabs. No kills, no combos, no nothing.
9.Spam up b and glide attacks. he really doesnt have an option to stop this either. Use it for the random chance of killing him with it.
10.Dont die from running up smashes....
11.dont die from random up smashes....
12.only die from perfectly comboed drills into upsmashes. once he realises thats the ONLY way he's getting a low percent kill, hes either going to go for more damage or hes going to throw out too many drills which are punishable.
13.If he tries to ledge gaurd you... KILL HIM. He can't obviously, he should know that but meh, he might get cocky.