game 2: ness was playing back a bit and also extremely weirdly kept going for djc magnet to fuck with your projectile game
-while i can't pinpoint it, something about your aggression feels... off
-it's almost like you give up on engaging with aerials once it doesn't work once, and you immediately choose a new plan of action without learning from the error
-obviously the arcfire tip but even you can identify that you straight up shouldn't use that so much
-ness specific matchup note, but arcthunder and thoron will only heal him for like 2% because it'll absorb the first hit and nullify the rest
-literally just slap him you outrange half his normals levin nair especially is kind of batshit
game 1 i'd talk about more but
as a former shulk main i have a whole DISSERTATION on that matchup
so ill continue this in a hot minute
SparkToday at 1:40 AM
GAMES 1, 3, AND 4: THE SHULK ESSAY
so as you can see from all of thsoe games shulk is an unga bunga menace to fucking society in this game
i actually hate playing this character because its so goddamn easy now, no nuance like there was in 4
literally the only thing he's going to do in neutral is enter speed art, get whatever he wants for literally free, and enter shield monado if he gets hit or is at kill%.
now let's break down how you played the matchup from the perspective of someone with extensive history playing both characters.
SHULK'S POV:
your robin is good with zoning, but the arts will still supplement my extreme range to still get me in on you. if i can pivot fsmash and catch you off guard with it, i can edgeguard you easily with fair; my main goal is to get you offstage with whatever strong aerial (usually retreating bair) or ftilt (which he did a few times.)
additionally, i have to be jumping; speed art's shorthop will get me over an elthunder, but it won't get me over arc or thoron. therefore, i should be in the air a lot.
when he's recovering, all i have to do  is wait for an option; fair will cover all but roll, and nairing on ledge will pressure him to act. otherwise, i can just airslash if im confident in the getup.
ROBIN'S POV:
your conversions need some work, and you need to bait shulk into playing against your zoning and not against his own art management. a lot of the time, you didn't respond to how the arts changed him as a character.
the thing is, shulk is the perfect matchup -- he will test you against every single stat-based archetype in the game.
to elaborate...
VS JUMP SHULK:
this interpretation of the matchup should be how you fight fastfallers like the spacies, roy, and obviously shulk, among others.
against this, what i usually saw you do was contest his jump-in with an arcfire from a distance, and hit-conversions usually ended after a single extra hit because of his increased fall speed. accounting for that, utilt > utilt becomes true against this art, among other confirms (thunder > dash attack or grab stops working because he falls faster, for instance, while thunder > thunder is better because he must deal with post-jump frames while you don't.
in short, manage projectiles better and look for anti-air opportunities constantly.
VS SPEED SHULK:
the archetypical rushdown character. they can be grounded, their jumps can be terribly short; either way, you're fighting against sonic, against pichu, against mario.
this matchup revolves around how you deal with really quick pressure that won't let up, as well as grab-chains. what you were doing was generally fine, but you can't fight him at all -- your attempts to hit him with a thunder while he's approaching doesn't respect how quickly and how easily characters like this can get in. sometimes, the best answer is simply to shield any time he tries to shorthop; keep in mind, his damage is reduced here too. if you can get a parry off, the punish is easy. a jab will cover most things these characters get in with (being as fast as frame 4, a hitbox would have to be out on the first frame after your parry), but slower options can even be sh. levin faired or naired. be extremely cautious of these characters and their burst options; you'll get blown up if you make a mistake, so respect what they can do at all times.
VS SHIELD SHULK:
not really much of an archetype, but i can lump this in with buster to some extent; the overlap here obviously being the super heavyweight matchup. in situations like these, shulk was trying to go in in spite of his extremely low ground and air speed and halved damage. to respond, you.. played the standard neutralgame and tried to throw decent-size normals at BigSwordMan that now takes zero hitstun. when fighting these heavy characters, there isn't a better option than (in shulk's case) waiting him out with thunder and (in every other matchup) totally walling them out. for instance, elthunder > arcfire can wall out heavies extremely hard; the added knockback from elthunder can easily give you the time to pressure with an advantageous arcfire. basically, tell people to fuck off more. heavyweights suck.
VS BUSTER SHULK:
see shield art; keep in mind you can get blown up extremely quickly and eat 50-70% in a few hits (like you did) because you weren't as cautious about the massive spike in damage. this also expands to not-too-slow bruisers; your roy, little mac, rob types. big damage; rely on shield and still wall out with projectiles, but if you notice something unsafe, delete them for it.
VS SMASH SHULK:
yknow how when you catch a jigglypuff in a hit, you always go for a kill option immediately, even if they're at 30? just because it might kill em off? against pichu, jiggs, etc. lightweights you get the idea, it's not as good to do stuff like arcfire > uair (your standard followup) as it is to just usmash them. they're a mile higher than anyone else would be now, and robin's juggles are batshit insane; you get so much more off of something just slightly different, but it involves the risk of fucking up the juggle thanks to how light these characters are.
there's my dissertation
TL;DR focus on the individual facets of each matchup and have a plan to overcome those specific traits. if you have the fundamentals of how to deal with a character's archetype, you have the skills and kit needed to murder the entire cast. also, think about a matchup from the enemy's view -- what are they looking for against you, and when? why? always analyze that between games to learn a matchup much quicker