My Take on R.O.B:
Defensive:
When R.O.B is coming at you, it's important to understand fully, what this person is capable of. I think that's the most important thing to know when fighting anybody. Just know, Each and Every High end ROB will start out with a Nice Laser, and then a Top. That is how the match usually starts out. Don't take that. Jump, or Spot dodge. Make a Mental note of when that Laser is charged enough to fire again. Remember, his Nair has Priority over pretty much Everything that Peach can Dish out. So, you can either Spot dodge, or punish him with Toad. His glide tossing is quick, but don't underestimate yours. If he glide tosses to you, Be sure to jump and float with the quickness, to get in some nice Dair combos.
Offensive.
It's important to know the Priority difference in this matchup. ROB Has Priority over All of Peaches main moves. Lets start with some Comboes for you to do, early on in the game.
Grab to Utilt.
Dair to Dair to Fair.
Glide toss to Double slap.
Glide toss to Slap grab, Dthrow and Utilt.
Glide toss to Foward B, to Fair/Dair.
Rinse and Repeat.
It's also very crucial to know, that Peaches Dair literally ***** Rob, considering that her reach is right out of Rob's reach to do anything but an Upsmash, and Rob's don't tend to rely on that. They assume you are going to fall, so that they can spot dodge, and then Down smash. Don't. Just Dair their lives away. At early and late percentages, this works like a charm. R.O.B has a Top? So what? You have Infinite Turnips. Make very good use of them, because every second that ROB is stalled, is a second for you to land a nice Bair, or a Clean Nair. Don't forget your Double hit Nairs and Bairs. Don't have em down yet? Get on your Wii and Get them down. Every percentage counts. It's not like you have the advantage in this matchup. Nair is also quite effective. Even when rob Spot dodges, it's hard to avoid it. And because it's instant, and Rob's attacks are delayed, it makes a great Punisher. He's coming at you with an Nair? Nair him back. It works, if you're fast enough. And Grab grab grab. Grabbing is a great way to mentally psych out a ROB, and rack up the damage for you.
Edgeguarding: K, there is not too much point in Fairing Rob, considering that he won't go very far, especially if your Fair is Stale. In addition, there isn't too much point in floating after him, considering that ll of his air attacks have priority over yours, and he can float over you and Gimp you. So, lets work this out from two different angles.
(When ROB is coming from Below the Stage.) This one is a bit tricky. Get out a Turnip, and glide toss one over in his direction. When the Glide toss is done, Turnip cancel a turnip, and then float to where he is below the stage. Drop another one and hang on to the ledge. More times that not, he will make it, regardless, but the Turnips will psych him out, and he just might get gimped. There is no clear way to Edgeguard him, but don't make it easy. Keep turniping him. Sometimes, if you get the Dot face turnip, it gimps him, because it makes him run out of Fuel.
(When ROB is coming from Above the Stage): This one is a bit easier. Take out a turnip, Throw it to an Fair, usually works out nicely for me. He Might try to attack while you are coming toward him. Thank god we picked a character that can change her movements in mid air. So you just float backward a little, then come back with an Fair. It may kill him, it may not, remember, That move isn't 100% effective against ROB, but it should still be done. When he is way Above you... Just let him come down. If you get to his level, he'll just Dair you or Nair you, it isn't fun.
Peaches turn!
(When YOU are coming from Above the Stage.) ROB's edgeguarding skill is Lolable, cause he can't. Just don't fall for his crap. Here is the Tricky part. ROB's Bair makes him fall at a 35 degree angle, so when you see him coming at you from the air, don't think of falling, cause he'll just Bair to Dair, which is really effective. So just stay straight, until you know that you can maybe Dair him while you are falling, or you can use mindgames to stop and start your Umbrella enough to get to a ledge.
(When YOU are comming from below the Stage): This is easy, you'll be fine. ROB can't do much. Drop a top? Dodge it. XD Just try not to use your float if you don't need to. If you do, that's okay, but it's really good to Insta float on the ledge. (Hold Jump while getting on the ledge and tap Down at the same time.) When you insta float, you can get an unexpected Fair, or some nice Dair combos. If you can't use your Float, just Jump up, and Dair as soon as the Immobility frames wear off. And then poof! You're back on the stage. There isn't much that ROB can do to punish you for anything, so don't be too scared to come back.
QUICK NOTE. ROB thinks that he is Cute, by Fairing you into Death. Don't let that **** happen. This is going to sound nerdy, But think of his Fairs as a Sin Graph. Notice how it goes up, then down, then up and down like a curvy line. Don't follow his patterns, Just Fast fall when he is going to hit you while rising with an Fair, And attach yourself to the ledge. =] Don't be scared underpressure, just Lol it off, and give the ROB a pat on the back for attempting to Gimp you. =]
Stages, Do's and Don'ts.
Do: Battlefield. R.O.B is not friends with Mr. Platform, but we all know that Peaches friend is Insta-tipper Usmashes on Battlefield. Also, we know that Turnip canceling is our friend on platformed stages. So Bfield is a great stage for you to pick. Equally, Counterpicking Pokemon stadium 1 is good. =D Gives Rob a Hard time to manuever, and gives peach great time to do some nasty Uairs on those plats, or some Dair combos when the map changes. The Windmill is Tangible now. You won't just fly through it, you can be saved by it!
Don't: You dare pick FD. That is pretty much asking for ROB to Own you. He has so many ways that he can attack you vertically, that it's crazy. The whole match you will get hit by lasers, and Tops, cause there isn't much way to avoid them. Equally, don't Counter pick Frigate. No ledges on one side, remember? ROB Does not have to rely on Ledges, seeing as he rarely needs one, but Peach does. No Frigate for you.
I hope this helps. Lemme know if there is anything I said wrong or whatev. But thanks for reading. =D