You go for an absurd amount of grabs. Fox really doesn't get enough out of his grabs to justify spamming them so much. His down-throw
sometimes combos into his F-air(or B-air), but it can be escaped too easily to be reliable. Grabbing is for when people like to sit in their shields(and shield grab you when you approach). If you do get a grab though, make sure you pummel for a bit (Fox pummels unusually quickly).
Dash attacks are really unsafe. You'll get shield-grabbed all game if you keep using them so much. Dash attacks are more of a whiff punisher than an approach tool. It can combo into up-air at kill percentages.
You should try and grab edge more with the illusion. You can get away with going straight for the stage sometimes, but anyone who knows what they're doing will get a hard punish on you.
And, finally, you use way too many rolls. Fox is one of the fastest characters in the game. When you keep rolling, you hinder his extraordinary movement. Rolling also makes it harder to get good punishes. If you roll past a Lucina's F-Smash, you
might be able to get a dash attack. If you shield a Lucina's F-Smash, you can get a free Up-Smash.
I really like your D-air usage (I don't see much of it) and you're really good at punishing whiffs with Up-Smash. The rolling and the Illusion (not grabbing edge) are the most important things though. They're the easiest habits to punish (and the most common.)
I suggest you watch a couple of videos in this thread to get an idea of high-level Fox play:
http://smashboards.com/threads/neve...ox-video-collection-thread-100-videos.392671/
Feel free to dispute anything I've said (if you feel it necessary).