Oh gawd you put my match against Bengalz up lol. That was a long time ago, and I did NOT know the matchup back then. I'm much better at it now XP
That match really shouldn't be used as a measurement of how to fight ZSS.
Anyways, ZSS is a very annoying matchup that I still think is in our favor. You just have to know how to play it. First tip I want to mention is that cowering in your shield is fine in this matchup, and I recommend it (with proper moderation of course). ZSS just has no way of pressuring your shield, breaking it, and her grab is just too risky to try. If she screws up a grab, that should be a lot of damage for free. This is my #1 here: Don't be afraid to shield turtle.
Now oddly enough, I don't know if you want to be constantly challenging her in the air. Her aerials are fast, and have a lot of range. Mostly zair. Zair is annoying. It's probably what saves her from having an even worse matchup here. You're not gonna outrage it, you're not gonna punish it. But honestly, I don't feel like you need to challenge it so much. Like I said, you shouldn't be afraid to play defensively in this match. Run in and shield a lot to approach her through her obnoxious zair. Then, it's a matter of making moves out of shield.
ZSS players like to toss out aerials out of SH when up close. You'll want to S/FH aerial out of shield with different timing based on when they habitually aerial. If they aerial on the way up from the SH, nair OoS after the hit. If they do it late for reaction, do your nair sooner. I recommend nair most for situations in which you accidentally trade. If you get under ZSS and you're feeling brave, you can try uair (her SH is tall).
Basically, build up your damage through defensive aerials launched from the close range ground. Don't just go full or SHing aerials willy nilly unless you wanna get paralyzed or zaired.
Now let's talk about her shield.
DO. NOT. TOUCH IT.
Utilt and UpB out of shield are very good and very fast. Utilt has shield frames and HUGE horizontal range. It sets you up in to uair juggles, and trust me, you do NOT want that. UpB we all know as the super quick, super strong KO move.
IMPORTANT: When you are at KO percent, do not EVER AERIAL ZSS' SHIELD. If you deny her one of her easiest KO options, then you make it significantly harder for her to KO you. Pair that with all the rage you have, her light frame, and our immense KO power, and we've got MUCH less to worry about. Don't be afraid to play super campy and lame if you're both on last hit status.
I highly recommend this video for surviving boost kick. But read my extra notes just under the video too!
Some things I just wanna add:
If you are INSIDE ZSS when she boost kicks, you can DI towards her to cross up and escape.
Mash air dodge; there's no reason not to. Sometimes not all of the little hits connect, and you can air dodge out of the last one.
Nick Riddle said to di
down and away to survive the last hit. While this holds true for surviving dying off the top, what if boost kick is about to kill you off the side? In this situation, you'll be dying SOONER. DI towards her if you're in fear of dying off the sides.
The funny thing about ZSS is that while she has a lot of low risk moves, a lot of her best moves (on hit) are super free if missed or blocked. So please, destroy her for missing that boost kick, or whiffing that grab. Ness has a powerful punish game, and I expect you to use it.
Other things about specific moves:
You can absorb paralyzer and dsmash. Dsmash is pretty impractical. You'll only get that on a hard read, but at least it heals a nice chunk. Paralyzer is what's good though. Smart ZSS players will use it in situations where it'll be harder to react with the magnet, so just keep your trigger finger ready so you can get the free food. Watch out for B reverses too. Make SURE you know how to magnet cancel. Mix it up too, don't always roll back. Jump, spot dodge, or even usmash out of it sometimes. A lot of ZSS players like to go in for the punish on the magnet (as they should).
Uncharged paralyzers don't combo into grab unless very close. Be ready to spot dodge or roll if you get tagged with one of these (but don't be predictable).
You can bat back paralyzers if you predict them, or they are really obvious with the charging. Don't get too cocky though, this is just a little trick you can try every now and then. Be ready to go for that grab if you get it though.
The best time to "punish" reckless flip jump use is to hit it right at the apex of the jump. At that point, she loses the invulnerability (yes, there's a TON at the start of the move, so don't challenge it there), and she cannot attack yet. It can be hard to react and get this hit, plus this move HURTS if it nails you, so don't be greedy with it. Just know that that point of vulnerability is there.
Be very wary of immediate tethers into flip jump right off the edge too. You don't wanna get buried and boost kicked to heaven. I very rarely try to challenge ZSS coming up from the ledge. Maybe that's my mistake, but she just has so many options out of it, and getting hit by flip jump hurts.
If you block a flip jump, ZSS is pretty vulnerable. She bounces off, and can still move and do things, but her options are severely limited. I'm not exactly sure of the entire list of things she can and can't do off the top of my head (don't wanna guess and be wrong lol), but it's still not a comfortable position for her, especially since her dair kinda sucks. Try your hardest to take advantage of her on the way down.
If you challenge flip jump, but are uncertain of your attempt, be ready to tech. It could save your life. In fact, always be read to tech if challenging flip jump. You don't wanna bounce up into a bair.
SH bairs are the most annoying thing up close. Space yourself properly if they're getting too comfortable with them, and go for the nair or uairs as a countermeasure. She can't zair you if she's facing backwards.
Dthrow. Uair, uair, uair, boost kick. I prefer to DI away from her to avoid uairs best I can. DIing towards her still subjects you to uair, but i just hate being over ZSS. You shouldn't really be caught by the boost kick that often if you DI away and air dodge smartly either. It's very hard to space a boost kick to KO a smaller character like Ness too (it's dragging little hits can be finnicky at times). Just be sure to watch out for fair out of dthrow killing you early off the sides. Still, dthrow fair hurts less than dthrow uair, uair.
That's all I've got for now. I haven't lost to a ZSS since that match of mine with Bengalz since I started thinking about this matchup straight