I don't remember exactly what I wrote before, so if I repeat anything, my bad.
Peach is one of those matchups I think is even in theory but much more difficult than it seems in practice. She can camp equally as well as Pika or better (heavily dependent on the stage imo), and although she can't kill until late, she can rack damage really quickly when you're at low damage.
A defensively floating Peach with a turnip in hand is what you want to avoid at all costs. When she has the lead and a turnip, Pika doesn't have any solid approach on her, and her aerials all autocancel, so you won't have many ways to bait her into something punishable. If you rush in, you'll eat one of three things: a turnip, an aerial, or a jab.
Pika's small shield hurts him a lot in this matchup..... if it's getting low, don't be afraid to run away and plank for a bit; otherwise, Peach will quickly poke your shield with a combination of turnips and aerials.
Spacing is really, really important here. Generally, Peach's aerials beat Pika's, so you don't want to try going aerial vs. aerial with her..... instead, I find that using my ground game and OOS options works better. The best place to be against Peach is above her. Jolts are easier to harass her with from the high ground, and her uair isn't anything special...... FF fair works much better when you're coming from above. Dsmash, uair, utilt, and fair are all useful moves against Peach (I like usmash too in this MU, but that could just be me =X), but you must space and time them well, or you'll leave yourself open.
At low percentages, both characters can combo, but I think Peach does it better. At mid-high percentages, Peach becomes a one hit wonder, and Pika takes the advantage when it comes to damage racking and killing.
Mind you, just because we have more raw KO power doesn't mean it'll be easy to kill Peach..... it's really really hard to land a kill move on her if she knows what to watch out for. Thunder is your best bet if you can send her up high (her airdodge is garbage), but other than that, you'll have to rely on a well-timed usmash or nair. Fsmash probably won't do you much good since she won't be on the ground that close to you.
All Peach really has is fair to kill Pika. On stages with platforms, she can tech chase you into a sweetspotted usmash, but otherwise you have to pretty much fall into it for her to hit with that. Her fresh bair is moderately strong, but it won't kill unless you're near the edge and/or really high in damage. Her fsmashes aren't very strong, though they will kill at high damage, especially if you DI wrong.
Off-stage, Pika wins imo, although Peach can make it annoyingly difficult to get back to the ledge if you're predictable with your QA angles. SB is generally a bad idea against her since she can float out and punish it or drop turnips on you in a gimp attempt. Try to DI upwards so that she can't reach you. When she's off the stage..... thunder walls are your friend.
This MU tends to be a campfest with both characters throwing around projectiles, looking for a way to get in on the other. Aggressive Peach is easy if you have the lead, but defensive Peach is a nightmare if you're behind. Stage choice seems to matter a lot here..... ****ing up her float and giving yourself the ability to take the high ground should be your primary goals. Stages I like are Lylat, Frigate, CS, RC, and Norfair.
Ratio is 50:50 imo.
Fair is also more tricky to hit with due to Pikachu's size
