Actually, in my match versus Cort I _only_ managed to win with IC's.
Fox versus Peach on Battlefield - Cort wins
ICs versus Peach on Yoshi's Story - I win
Jiggs versus Peach on Mute City - Cort wins
Yeah, kinda weird.
Basically, I think the IC's just have massive disadvantages... it's not unwinnable, just.... ridiculously difficult and relies on a LOT of capitalizing on mistakes. As far as your moves go...
F-air - Use this when Peach is on an even horizontal plane with you... if she's floating low or she's on the ground, retreating with this and using VERY cautious approaches works more than most of your other options.
B-air - This move should really work a lot more than it does. Often times you trade because Peach is such a skinny target. It's got good potential, and I think it works better while retreating than advancing.
U-air - Probably your safest move, and the one you should keep an eye on landing the most. It's the least likely to lose to any of her stuff, and if you space it right and can get directly beneath her when she's NOT downsmashing on a platform, then you shouldn't have a problem getting some damage and putting her in a bad position. You can only use it when she's floating high, however, and that's a big problem. A technically skilled Peach can just float low with f-airs and n-airs, or float at a medium height and kick your face in with d-air. If it connects, she gets n-air or d-smash, and that pretty much wrecks you for the stock. U-air is hard to land. I would say the best time to land one is when she's on a platform and pulling a turnip. She can't CC it into d-smash because she's holding the projectile, and if you know when she's going to pull it, you can wavedash in with relative safety and get to an advantageous place.
D-air - I ignore this move almost completely because anytime I try to utilize it, it gets CC'ed or the Peach just recovers before me. The only time it really would work is if she was close to the ground and you could guarantee connecting with it.
N-air - Uhh...? This move has so little priority that trying to use it against Peach is dangerous and kind of foolish. Only use it if you can combo into it and have no other good follow ups. Most of the time, she can just CC it if she's on the ground, or just n-air or b-air you out of it if she's in the air. Pretty much just forget about this one unless you can't hit with anything else and you KNOW you're safe. Otherwise, you'll probably regret it.
Blizzard - So useful. Having Nana do this is probably your best defensive option, since the only way Peach can beat this is by floating over her head. If you've de-synced Nana into it, you can use any of your maneuvering abilities, and it's a bit safer since Nana created a dead zone for you to work with. If Peach runs into it, you can try and space a smash or aerial or--if you're lucky--a grab.
Iceblocks - Not quite as useful, but still handy. You want to fire these above and in front of Peach mostly, because that makes it less likely her n-air will work against it. She could probably u-air them, but you still might get her to crash into one, and all damage is good. Work with platforms when you use these, because if you have to spend a lot of time landing then Peach can get around them and make you very, very sad.
Shield - Gets its own section! Light shield, ALWAYS. You will get clipped with d-airs, turnips, b-airs, and d-smashes if you don't light shield 99 percent of what Peach does to you. D-air to d-smash will **** your children and haunt your dreams with the mutant offspring if you don't light shield. The shield also pushes you away from her, which lets you recover from the offensive.
Up-tilt/Up-smash - These two are pretty handy against Peach because you can land them with simple wavedash mixups. If the Peach you're fighting is defensive, then wavedashing in--backwards is best, IMO--into these moves can hit her if she's a little higher than d-airing height. You have to be fairly unpredictable with your wavedashing patterns, however, or she'll just hit you out of your attacks. Up-tilt is nice because it sets up for up-air and does good damage, and up-smash reaches around your body and KOs better.
F-smash - Useful for wavedashing in with, again, but this works better when she's lower to the ground. Very laggy, use cautiously, and space well with it. You still might lose, however, should the Peach f-air or d-smash.
D-smash - I don't recommend this as an approach simply because if d-smash will connect, then a grab will too.
D-tilt - Ick. Little knockback, damage, range, okay for speed but can be CC'd. It has a useful popup feature should the opponent decide they won't crouch cancel it, but... you would probably rather grab any time you could connect with a d-tilt.
F-tilt - I would say the same thing about f-tilt that I have about d-smash or d-tilt, except it comes out faster than a grab and reaches pretty far. It's less laggy than d-smash and has better knockback than d-tilt. It can also be used to set up the f-tilt guard de-sync, although losing Nana's damage and knockback makes it worse against Peach.
Jab - This is a great move against OTHER characters... but Peach will CC it and you will pay for it. It doesn't have the range of f-tilt so you have to get in closer to land a hit that will get you badly hurt... so I recommend just ignoring this against her.
Grab - Needs no real explanation, does it? You can't get obsessed over landing these even though they're your deadliest weapon. If you do, you will ignore the other aspects of fighting Peach, become predictable, and get punished hard.
I'm spent.
