"Retreating fair should beat out bair or fair"
this would be true, but ganons don't approach..it's just a lie they want you to believe...i've changed my mind a lot about this in the last week or so but basically fear will get you killed...
i would dash dance around and get a few grabs so that they start playing for space and trying to use jabs some...jab is good because if they are jabbing you can..
sh approach...i would do the aerial on the way down...
now you're asking..what happens if they are in the air already and going to trade with you...the answer is you just don't care...eat a fair or bair...learn to DI....try to land spaced fairs into shield pressure on them or nonspaced late fairs into dash through or nair into uptilt...the reality is that ganon crumbles ten times worse than marth when marth gets inside his max distance range because marth can spam uptilt after moves...dashdance circles around him, etc etc.
so the worst possible thing you can do is try to only camp him...dash dance camping is good..but if you are only camping the whole time
you will keep losing space if you never commit and then get boxed out at the ledge.
however, if you approach instead of being a coward..when you eat a fair/bair you won't be at the edge of the stage, and you can DI and still recover....
as an added benefit, if you actually tip a fair or hit a nair you don't have to combo him all the way across the stage but can just hit one or two aerials and then get him offstage with ease.
unless you have practice using reverse up b to guard his down b recovery, then i don't recommend small stages.
big stages are also good for learning not to fear him and working on DI because when you're wrong you don't just instantly die...gives you more chances to learn when to approach
on recovery, high up B's into fall to the ledge aren't as risky in this matchup because the only thing he has that he can use quickly from a grounded position that covers horizontally is his ftilt..
so you need to risk doing this occasionally since he can waveland off into reverse upairs.
what chip said in the last line basically translates to "everything you do will combo ganon except for noncommittal nairs"
i only mention the noncommittal nairs because back when i was trying to outcamp the ganon like everyone said I kept trying to hit nair but it never seemed to combo very well...the whole spacing them out and DIing out tends to make them not combo that well
also, don't keep trying to force grabs after they start jabbing it's better just to start approaching in that situation..though obviously you could grab them after the jab it's easier to just jump in there and get things going.
oh and if you're playing kage you are just going to die probably...good luck...when you get super good at the matchup post on here and enlighten us...normally i don't write so much, it's funny..there are matchups i know really well, but i post on the one that i know the least...i guess it's cause i was having a lot of problems with it and was doing it all wrong so i want you to at least have the balls to commit instead of playing scared and trying to outcamp the ganon (don't get me wrong, i wholly approve of dashdancing and making sure the ganon stays honest..just don't try to play a spacing war against him as if he were jiggs [except at low percent for those grabs])