It does not beat his up air if he spaces it correctly, which is not difficult to do to someone who falls as slow as peach.
I think the safest place to be is the ledge, but I always have trouble getting there. MK can do so much... Praxis, llod, someone good, get in hereeee
I feel like I asked this question a while ago, but the responses I got weren't too clear. Also I've been criticized several times by several people about how I'm not too great at recovering back to the stage. But, I have thought about this a little bit, especially against MK, so I do have a little input.
Common things MK can do to edgeguard:
~Shuttle loop: An easy gimp if you're not careful. Shuttle loop has wrecked me several times before, especially at not-too-wide stages like YI. MK's get under/a little in front of Peach and shuttle loop. If it hits, then it truly is an easy kill.
~Dair: Often when Peach is recovering from below. If hit right, then Peach gets gimped. MK has a lot of jumps and a great recovery, which mean he isn't afraid to chase you for the dair. Don't feel too safe when recovering from below. Dair can also stage spike/send you beneath the actual stage.
~Fair: This happens a lot too. MK jumps until he's at your vertical height and fairs you, sometimes killing you, and sometimes pushing you back.
~Uair: Usually when MK can't get to your height, he uair. Simple
Things Peach can do to prevent being edgeguarded:
~Dair: Dair is pretty useful, although it is predictable and can be outspaced/outtimed. Dair beats shuttle loop when MK uses it in the air, which is pretty helpful, but I believe MK can space it to hit the front of Peach, not her feet (so dair misses). If dair hits, then it's pretty easy to get to the stage.
~Fair: Very useful when you know MK is gonna chase you. A lot of people think you're going to run away, so chasing them instead can give them a surprise. One hit gives you an easy recovery
~Air dodge: Not the best move. If the MK is jumping/falling, waiting for you to do something, air dodging gives him the perfect chance to hit you with... anything. Air dodging can be used to try to predict MK's attacks, but if it doesn't work, then you're screwed.
~Side-B/Uair/Bair: I've been told that these moves help by changing your momentum, confusing MK, and giving you a chance to get to the stage. I haven't used these much, but I know some people do. It's usually a better idea to try to get the actual hit, though, to give you a safer journey.
Up+B: The obvious recovery move, and sometimes you can use it like Snake's Up+B and go over everything. The problem is Mk can get up there and shuttle loop/uair you out. Peach also falls pretty slowly, even when FFing, so be prepared for some serious changes of direction when trying to get to the floor.
Ledge vs On the stage:
~Ledge: I love the ledge. Getting onto the ledge gives you those amazing invincibility frames, which can easily get you back on top of the stage. Going for the ledge is best when recovering from below, and if you can up+B onto the ledge, then you don't have to worry too much about being edgeguarded. The ledge helps, because if you weren't able to hit MK away from you when recovering (which is harder when recovering from below), then the invincibility boost is awesome.
~On the stage: I prefer going directly to the top of stage if I
start recovering from somewhat above the stage to extremely high. If you can get past MK with a dair, fair, or whatever, and you're falling down to get back to the stage (as opposed to jumping/up+Bing), then I prefer going directly to the stage. This gives you a chance to get a turnip, run away, or whatever.
Overall:
For me, MK is the hardest character to get through when recovering. He has a billion jumps, and can hit you in so many ways. As I said, I prefer going directly to the stage when I start high, and I prefer going to the ledge when I start low. From the ledge, you can get up in a lot of ways, so that isn't too much of a problem. In my opinion, the most important part is to hit MK in any sort of way. If you can get that, then you honestly have a free ride home. Of course, MK can chase you again, but you at least get the head start. MK can be beaten