Ganon outranges Ness super hard, take advantage of that.
As for Ganon's bad matchups, TheFatHen:
Falco and Fox for obvious reasons, Ganon does not deal well with projectile spam and zoning from Falco, nor does he deal well with Fox's shield pressure/offstage gimping game, considering Ganon's awful recovery. These matchups are playable, but favor the spacies. I'm inclined to think the Ganon Wolf matchup is closer to even, because Ganon can CC Wolf shine and Wolf's projectiles aren't as effective as Falco's or Fox's IMO.
Ganon also struggles with Mario a bit, since Mario can cape his recovery, combo him to all hell, and zone him with fireballs. That said, 3.5 makes it a bit more bearable for Ganon players.
Diddy used to demolish Ganon, now it's a bit easier but still in Diddy's favor. Bananas are still bananas and Diddy still has his gimp game, he just has to work for it a bit more. Definitely doable for Ganon, however.
Sheik absolutely messes Ganon up. 0 to deaths and a ridiculous gimp game all over the place, not to mention (not 100% on this) Sheik can duck under Ganon's grab. This is one matchup I refuse to pick Ganon into unless I'm significantly better than my opponent.
Link/Toon Link both zone Ganon fairly hard, and can combo the mess out of him. Tink is a bit easier because Ganon's aerials outrange Tink's, but the projectile spam is real, and that's all Tink needs to get in. Link straight up dominates Ganon, however if Ganon manages to get in, he can most certainly mess up Link's day. It's getting in that's a problem, and a very good Link simply won't let that happen easily.
Mewtwo is still fairly rough, but playable.
Lucario could be bad, but I'd have to see where the more experienced Lucario players take the character. Lucario throws down some ridiculous pressure, on top of a reliable projectile game and some crazy combos. I think this is playable for Ganon, but most likely pretty rough.
Ivysaur can just play a spacing war with Ganon, except she has a healing ability and a projectile. Ganon can reflect this pretty reliably though, so I'd say this isn't too bad, like 55-45.
Charizard, in a lot of ways, is like Ganon with slightly less potent killing power and a marginally more effective recovery and grab game, in my opinion. 55-45 as well.
Samus is still Samus, and Ganon gets absolutely wrecked by projectiles. However, this is another case of Ganon's aerials doing more work than Samus', and with Samus' recovery being nerfed this patch, she is now easier to gimp. I'd have to play it out a bit more, but it could be approaching even.
I think Dedede has a good matchup vs Ganon as well, outranging him in many ways, along with a half decent projectile and a more effective recovery. Obviously still playable for both parties.
Ike may be looking scarier for Ganon this patch, though I'll have to look into it.
Game and Watch is looking to be top tier this patch in general, and the ability to keep Ganon out of his space until he finds an opening to 0-death him is extremely potent. Ganon can kill Gdubs extremely early, though, so play this matchup carefully on both sides.
I'd say that's about it in terms of blatantly bad matchups. Everything else is even or favors him. Regardless of how bad it is I'd say try to adapt, because a lot of the time you're losing to the player, not the character. Make sure it's pretty much undoable before you consider picking up a secondary.