Ganon online requires lots and lots and lots of muscle memory.
I play my ganon online all the time, and I've thunderstomped falco's out of phantasms and done other ridiculous things that don't make sense. If you want to be good at online then close your eyes and listen to Ganon. Try to time his thunderstomping perfectly. It helps offline too, but online you need that timing, because the normal visual cues that you get to start your next jump after an AC is not there. It's delayed. So most people are really slow online. I used to always screw up my ACs.
I agree with this statement and would like to add that I think that online experience can come in handy offline in mysterious ways.
For example, have you ever had to play Brawl on a laggy HDTV? It can be frustrating but I think that for people who play online a lot, the adjustment to input delay is so much smoother.
Here's my story (you can stop reading if you want):
So I live in an area where nobody takes Brawl seriously and I have been playing online a lot to get human experience. One day I go to a tourney out of state and find out that I will be playing Brawl on a big projector screen, which is notorious for input delay.
I start my first match against a super spammy Wolf and much to my surprise:
I COULD ACTUALLY APPROACH WOLF!
On a laggy projector, I could walk right up to Wolf power-shielding the entire way through. You could only imagine my surprise after all the months I spent on wifi struggling against all manner of projectile to come to a tournament and rip apart blasters and arrows and such with my mighty shield, and on a laggy projector screen!
That is why I think that online experience is frustrating, but can be a great trial-by-fire approach to improvement (especially without offline people to play in the local area).