Here you go. Just the thoughts of a rob main since s4.
Killing:
I actually really like ROB's kill potential in this game but it isn't any one thing.
I will say his strongest place to secure stocks is at the ledge. Though ledge isn't as punishing as it was in smash 4, ROB can still do his neat little "cover everything except stall" thing which is executed by facing toward the stage, short hopping and z dropping top right at the edge, then landing and using up smash to cover roll up. If timed properly even if they neutral getup or jump getup the top will launch them into the up smash which true combos. If they attack up they may or may not hit the top out of the way, it's inconsistent. Either way they can't punish up smash then (In s4 you used to be vulnerable before attackup so the top would hit you anyway... good times).
Anyway that's really the ideal setup when the opponent has to take a long time to recover, usually you can't get that set up. In that case ROB still has some potent options at ledge. Arm rotor is one example, use it so it will cover a roll, jump and neutral getup and make sure to do the input away from stage (the direction of the initial input determines which way they get launched, nothing else). It is extremely committal though so I recommend learning the kill% range and only using it when it can net a stock.
Other areas on stage, ROB does have to work a little more for a kill. I usually just try to convert to an offstage situation with top, because onstage it's like... spot dodge down smash usually? And close range isn't exactly ROB's strongest area so it's less than ideal.
ROB also has that neat kill setup but I've only actually executed it in a match a handful of times. Anyway it ends in arm rotor offstage and that even when used on its own is not a bad idea. ROB will recover anyway and hopefully if you're good at recovery mixups (since he has so many of them) you can do it safely so it's pretty low risk. You have to read their recovery path pretty hard but hopefully some projectile conditioning helps things there.
Also regarding offstage recovery reads, people will often double jump back to stage against ROB and if they're past like 90% you can just hard commit with a dj up air where they will be since that's a long lasting move that doesn't require too much timing precision to use.
Speaking of up air, another key way ROB kills is with dthrow, as much as people (like me) hate it. Opponents do really have a "mash" stat that you have to get a feel for and it will determine what you can try with dthrow. Anyway, even if they're a god level masher, dthrow -> uair will kill above 150% or something. Obviously just use uthrow if you start getting them to that percent though. If the opponent stalls in the bury you can call it out with a dsmash or if they're big enough, usmash (smaller characters' grounded profiles just completely get missed by usmash if they stay in the ground the whole time... someone should make a list of that some time)
Anyway yeah overall the way I mainly secure kills as ROB is to force a ledge situation by landing stray projectile hits and using ledge trapping. There are other ways to do it obviously but I think he's strongest here.
Projectile usage:
This is an art, not a science. It all has to do with watching how the opponent reacts to your options. If they jump over things to try to get in you can punish it hard with sh top throw forward. If you throw it almost instantly it will sail right at most character's jump height and also hit platform, a very good option and generally why top in the hand is better. However against shorter characters you definitely want to put the top back on your base since they can run below thrown top. This is something you need to be consciously aware of and switch based on matchup, don't get burned by a tiny pichu running under top throw too much. Anyway if they shield it's more of a wash as I said before, but it conditions shield at least so if you use landing top a lot you can tomahawk grab at a later time, maybe when it would secure a kill.
Speaking of landing top, it's good. Particularly to cancel hitstun so you don't have to tech when hit by low angle attacks. Teching is bad and slow, no matter how cool it looks. But anyway even in neutral you can b-reverse top to shuffle around and shield cancel it. Run off battlefield side plat to b reverse top is a good way to both land safely and agress. Also remember that you never have to actually fire top when you start charging it, it's as free to cancel as samus neutral b or whatever so you should use it for movement mixups too.
Anyway you're going to be just firing these things off throughout a match, it happens. I'd recommend using them when the opponent is landing or you have tons of stage between you though. Especially laser, there is approximately one year of lag before that move fires. But the top actually does kind of put ROB in a bad spot if it's used poorly since it has decent lag. I like to use retreating jumping tops and lasers so at least my opponent can't directly punish me if they jump in or try to roll through. And once you hit with top you can usually pick it up which is when you can do fun stuff. If you watch WaDi play you'll see he likes to go for top down throw above the opponent into imagination. It's a slow traveling projectile that guards you and can lead to combos, so that's a fun use but maybe a bit impractical to set up most of the time. Throwing the top upward and using it as a "safe zone" since the opponent won't want to be there when it lands is another fun tactic, but perhaps most practical is just keeping it as a threat and approaching with z drop recatch nair and so on. ROB can really play pretty aggressively with a top in hand. And of course you can always bet it all and throw it, but don't throw it willy nilly or at the same time in the same situation over and over or you'll be forfeiting ROB's most powerful tool.
Overall I think if you play against Rosalina a lot she will teach you the right and wrong times to use projectiles. You do still want to use them against her, even the top but especially laser since it can launch luma pretty consistently and if you mess up she can't get it in her hands like top, but if you just use either in neutral all the time you won't get anywhere. She will punish you super hard for any top usage even. But I've played whole matches with rosa players where they never got the top in hand once and I still used it semi-regularly. It's about selecting the right time use them. They should be used when you've already applied pressure e.g. when she is in a landing situation or cornered. In these cases it's not "free" for her to use down b since you can theoretically punish it if you go for a normal attack. You can apply this logic to people without reflectors or her thing too, whenever it's not "free" for your opponent to just shield or avoid your top or laser, that's the perfect time to strike. So yeah you need to mix them in with nair approaches and so on for them to really come alive as true pressure tools, not just free damage since they won't be that except against really inexperienced players.
Juggle escape:
This has long been one of ROB's big weaknesses and it really pairs badly with his huge frame. There is no easy escape option for ROB truly. Yes nair is the best but it doesn't win all the time and it needs some time to wind up. The best part of nair to actually try to land with is the last portion of it when the active hitbox is right below ROB actually since it hits a nice range and lasts surprisingly long. It also happens to be near the autocancel window and be good to combo into since it has more frame advantage so there you go. But if the opponent has some big burst option nair can't contest like Joker up air then you should probably try one of ROB's many alternate recovery options.
One of my favorites is to save double jump but upb/bair several times way above stage height and beyond where they can reach then fast fall neutral airdodge after you've sufficiently confused them about when you will land. A lot of players expect an immediate or double jump then immediate attempt at falling so if you can confuse their timing you will generally have a better time making it through. This is also true on the ledge btw, don't ever get up with the same timing twice!
Anyway you can also use ROB's dair to stall yourself and punish your opponent if they try to hit you where you would fall. It's mostly useful to also drift during the animation though so you can land out of their reach while your opponent is trying to get back to the ground to follow you. If you do this any more often than "rarely" you will just get read on it and it's very laggy so yeah, don't do that.
If you have some horizontal distance between you and your juggler, both fair and bair have uses in helping you land. If you can find the time to execute a bair aimed away from your opponent from fullhop height or lower, they'd need to be really on point to catch a landing after that. Fair is all about covering your landing and it's pretty long range, you just throw that out of a fast fall to hopefully beat or at least trade with their aggressive option.
And then directional airdodge is a thing but kind of a big mixup that can get punished hard. Sometimes against pichus who hold forward and try to fair you off the level, DADing into them just gets you through them and gives you stage control pretty safely though. Or they will combo you so you can't airdodge or hit the endlag of your airdodge with drift in bair. No one said it was easy. Anyway airdodge to platform ("waveland") is also a good option if you can execute it properly so that you minimize lag by landing cleanly on it.
Also don't be afraid to just retreat to ledge. Yeah ROB is big but ledge jump nair is a thing and all those top setups on ledge are also important. And you can still neutral getup and roll too, which might just be your best bet against people who can juggle all day.
Nair:
Yeah, it's good. Don't even get shook if your opponent manages to parry it once or twice. As long as you have confidence that you can mix up the timing you use it in, which is fairly easy to do when you just alter your fast fall timing, no opponent can consistently parry it no matter how good they are and that's more of a cheeky option that might work some times. Beyond that you have to try to space nair so you can't get hit by their burst option of choice, maybe it's sh nair for most chars though. This can be tricky since good opponents will run in and put their shield right below you. In those cases you need to think about mixing in tomahawk grabs so they can't shield for free or just using dair and getting out of there every now and then. Anyway have confidence in nair and use it in neutral. Nair is like Ike's nair in that you hit more often with it the better you are at eliminating all your opponent's other options. I mean, when do they get hit by nair? When they try to roll, attack, or jump. When do they do that? When they're afraid of projectiles or grabs. So obviously you need to give them a reason to be afraid of those options, and in turn the potency of those options feed off fear of nair. Nair is more free than the other options so it tends to be your "spam" option but you can't rely solely on it.
Stage control:
If you find yourself getting run down by an incineroar you are not challenging their space enough. ROB has a pretty quick dash attack and a nice short hop fair. Yeah he doesn't want to be super close to the opponent but it's not the end of the world for him either. Use those burst options to make the opponent afraid of just chilling near you and they will be forced to give you more stage to work with. But they're strictly mixups. No good ROB will just dash attack all day. It's all about putting the possibility in your opponent's mind and punishing them with it when they DON'T have that possibility in their head. Also putting up a nair bubble generally wins you some stage. That is to say just using nair so it might hit if they approached into it, not actually trying to hit with it directly. Top also creates stage control if used from far away since they have to try to catch it or jump over it. Both can be punished. If they like to dash attack to pick up top you can just shield, that's a really low level play after all. If they try to go over top you can anti-air. I guess if they catch it with a retreating aerial or something you actually have to start watching out for top placement more and not leaving it where they can grab it, depends on the opponent though. Also just top in the hand is good, throwing it down to protect yourself deters like, pretty much any approach your opponent can think of. Only has a hitbox for a short time though, but good if they're coming in hot. Anyway if you do find yourself in CQC against anyone don't forget that dtilt is blazing fast. You can use that to get out of a situation where you find yourself cornered usually, and if you get the trip it true combos into top so that's fun.
Okay that's enough. Hope it helps.