It seems ZSS's flow chart going in for Falcon generally revolves around nairing and stunning to create safe space away from his shield, with the occasionall nair or zair approach. An interesting tidbit i've found comes in handy is that with characters like zss and sheik, who hae to be falling to make their frontward aerial approach optimal, is that if you predict when they are going to shorthop nair, you can approach with a forward moving nair up from the ground. nair will actually come out faster then ZSS's nair or sheiks fair because you're doing it immediately, while they have to wait a certain amount of time before they can use the move to cover their fast fell landing. As easy and standard as it seems, it's really hard to do a forward moving nair, at least for me. My very hard pushing instinct tells me to nair right where she would be if she shorthopped straight up and landed right where she started, but most all good ZSS's will move backwards in the air when they see you approach. Pay attention and make sure you move forward as much as you can when you nair at her. It's a precise finger movement and a little bit harder of a commitment, but ZSS's will usually be hesitant to grab, and if you can react fast enough to landing behind her you can tilt back towards her to cover any kind of punish, and hold the old reliable jab afterwards. approaching with a short hop RAR can work as well but it is harder to pull off and takes more precise timing. Up air can work in the same effect but has less range then nair, has less follow ups at low percents, and is extremely hard to get to come out that low. Dash attack can also beat it out if spaced and timed relatively correct, but is a guessing game to follow up and usually lets her create space away from you.
Grabbing ZSS is hard for falcon. ZSS doesn't have enough landing lag on her nair to punish, and when she isn't doing that she is usually jumping away. The better the ZSS is as a player, the less likely they will be shielding when we want them to. The best ZSS's will almost never stand still no matter how much you bait them (barring whiffed grabs and the such), raw grabs are a bad idea. Grabs are best to go for out of back airs. If she is pressuring the back of your shield. catch her shorthop with a bair out of shield and immediately go for a grab, though sometimes not completely guaranteed, bair is the best setup you will get.
Comboing ZSS seems to be a little less stressful than most characters for falcon. She's got one of the easiest weights to down throw->knee at kill percents, and she doesn't have many low frame moves to break out of combos, which make her easier to downthrow->up air->knee, and bait airdodges, which is pretty nightmarish for a character with her recovery. If you havent seen Max Ketchum vs Nairo's zss, you need to.
Whenever ZSS is above you she can use a variety of tools to get back to the ground. Her Down b Has invincibility frames, and i'm not sure but it might have a pretty quick start up/ ability to get out of being comboed. She will almost always b reverse away from your approach and release the stun right before hitting the ground to cover her landing. you have to be very patient and reactive to punish her. follow her in the air, bait her to down b and punish it. bait her to b reverse and quickly change directions and be ready to punish that.
Powershielding the stun is key if sheilding it at all. Most lower level ZSS's/ZSS's with little matchup experiece will try to gra you after stun hits your shield every time, which is easy to dodge and even easier to punish. Good ZSS's will stun your shield a couple times and try to read or react to what you do. They have to run it into a rock paper scissors game or just not approach afterwards at all if they're that lame. Either way falcons best tools to deal with the stun is to powershield it and if she's close: tilt, nair, or bair out of shield. i find tilting out of shield to catch her approaches and short hops will really catch the player off guard the first couple times and can be a good setup for grab if they aren't prepared. If she's far away: full hop toward and react, run toward and react, or make a hard read and go in.
Beware ZSS tilt out of shield and her pivot tilts... just her ftilt in general. More and more ZSS's are using it lately and it seems the better they get, the better they use ftilt. it's not really punishable if it misses unless it barely misses and you dash attack or something. the only real punishes i can think of is shielding it and dash attacking/tilting out of sheild yourself, but i haven't dealt with it in a while and can't really remember all it's properties very well.
When it come's to gimping Falcon, ZSS honestly really doesn't have any reliable tools besides her zair trump bair, which is insanely deadly. her down b has to be super precise and started almost before your up b. if you mix up when you're going to up b and recover low mostly, then you should be fine. i've never seen the side b be used o edge guard so i dunno about that. Most ZSS's i've played will almost always try to time a zair trump bair, or stand on the ledge and try to react/read with a down smash. not much off stage trouble.
Gimping ZSS is usually pretty hard, but there's not much harm in trying. you have to read whether or not she will try to down b on th the stage, which can be punished with like anything, but usually ends up with her being back on stage. if she doesn't down b then she'll almost definitely tether. If you have really good timing you can stage spike or even fall off immediate dair her tether. Almost no ZSS's will up b back to the ledge unless they have to, but if they have to, be ready to dair the juicy foot hitbox that comes so far above the ledge before she grabs it. You have to space it so your dair hits without you being hit though which can be a challenge. falcons dair exteds his hurtbox downwards, but not as far down as the dair hitbox, and ZSS's upper foot on her up is a hitbox AND a hurtbox all the way up. So you have to try to make the disjointed hitbox hit that, same thing with little Mac's up b.
