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Shield
A lot of improvements were provided to Bowser's move-kit involving stronger damage, stronger knock-back, & faster game-play overall. Shield reduces all the damage Bowser puts out, I won't discuss about every buff Bowser received though, too many buffs.
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Buster
With Falcon's buffs to his Special moves, the changes done to his D-tilt & U-tilt, & a huge disjoint added to his FSmash, Shield will help against CF. Falcon is practically a rush-down bruiser that received more KO power, so he'll stay close while he can, though if a spaced Shulk shuts him down, changing to a different Art is suggested.
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Shield
Charizard got a few revamps noting his DownB now being Rock Smash, & his replaced SideB with Flare Blitz, which is single-handedly the main reason you wanna stick with Shield stance. Flare Blitz is hard countered by Shield alone, making Charizard mix up his game against Shield Shulk. Mostly Charizard is heavy, hits hard, & now has a reliable horizontal recovery move that can be used recklessly against us.
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Shield
Dedede got heavier, more KO power, & stronger damage % on some of his new aesthetic changes, like all the other Heavies got.
Gordo Throw is asking you to VIsion counter it, unknown of what result will come out of that.
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Speed
Generally Jump is an alternative, however with the steady all-around buff Diddy received to all of his aerials becoming faster & stronger, & the nerf to bananas, Diddy's ground game was more nerfed, trading off with improved air-game. It also doesn't help that some of his moves get extended range on them, such as his F-tilt.
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Shield
Like all the Heavy-weights, DK gained more strength in some of his aerials, but mostly his moves come out faster than before, including his general game-speed. Giant Punch wound up 9x KO's fairly early, & since the move comes out faster, this move alone plus DK himself is a threat.
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Buster
The only projectile the doc has is MegaVitamins, & as long as you avoid getting hit by them, you're basically good to go. Dr. Tornado is back & helps the doc recover slightly, including general buffing to several moves by either getting stronger, or more KO power added. Dr. Tornado is a ground option I see docs using, so just Vision Counter this along with any Pills he throws your way while aggressively approaching behind that pill, & you're good.
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Jump
Falco got several changes to some of his aerials that connect better with slightly less landing lag, so his air-game for that matter seems a bit improved, though his D-air's start-up is a lot slower, but more powerful, including his USmash becoming stronger. Falco's Phantasm doesn't leave him helplesss, plus Fire BIrd gets more distance. Use Jump to edge-guard Falco shutting down his buffed recovery & ruining his options. His Lasers landed will lag, & cannot shoot as frequently, cutting his aerial coverage with lasers in half, making Jump an ideal Art to use against him.
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Jump
Same scenario for Falco mostly. His lasers used upon landing have lag, his phantasm doesn't leavel him helpless, Fire Fox's distance is even greater practically to Melee status. Only a few buffs to his KO power & strength I've noticed. Falco = rinse & repeat.
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Shield
Another Heavy-weight scenario in Sm4sh. Heavier, stronger, & faster.
A lot of things about Ganon got buffed, but some note-worthy setbacks are present. One notable change is being able to tech off of Flame Choke's slam, teching or tech rolling helps mitigate the chases, but now it becomes a tech chase moment where you can't be too rash & predictable.
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Buster
G&W did get some changes here & there, slightly buffing his ground game & his air-game, but to boot, nothing too spectacular of a gain or loss. Some nerfs were made to his N-air & D-air. U-air got some of a buff, but avoiding damage & dealing it out is recommended. Esepcially since G&W is a very light character. Buster works well against Light-weight cahracters, so let it rip.
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Shield
Things seem unchanged for Ike from a quick briefing, but his QuickDraw not putting Ike in a helpless state, & bodes well for Ike to not be gimped by physical contact halting it previously in Brawl. Yet it's undeniable Ike has KO power, strong attacks, being heavier. Resembling of classic heavy-weight quota.
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Buster
Apparently being called the Queen of Air, yet when she touches the ground, she isn't there for long. A couple of her throws got stronger, few moves got sped up, & her signature B-air got increased KO power, not to mention her Rest can be combo'd more easily while having the ability to stop her Rollout in mid-charge. Overall I feel the few times she makes any move on the ground, it's Dash Attack, Jab, roll to U-tilt, or Rollout, which can be VIsion countered with the forward input to quickly dash through her resulting in a stronger counterattack with more knock-back. Take to the air & overpower the Queen of atmosphere.
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Buster
Inhale, Hammer Flip, Final Cutter, & Stone can all be Vision countered. Yes inhale can too, the wind-box that sucks you in can be countered. Hammer Flip is an easy wait-and-watch move that you just wait for the first active frames of the move proceeding to its hit-box, that's when a forward input Vision wrecks Kirby's world. Final Cutter as a projectile can easily be shielded or Vision countered if you're relatively near Kirby that your regular dash & slash counterattack would reach. Kirby overall moves faster on the ground like others do, & he got buffs to his Uthrow & other moves such as dash attack & USmash, but nerfed on the ground as far as his attacks involving his feet go. On top of his leg attacks shortened & grab range decreased, Kirby's a light-weight character, making Buster more worthwhile against him.
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Speed
Link overall got a large amount of buffs, mainly his clawshot, Master Sword's reach being longer, & his Specials beefed up in some way. His UpB Spin Attack apparently was restored to Melee status.
Bow charges quicker doing less damage, Gale Boomerang overall got better, & his bombs doing more damage, yet with added gravity to them, their thrown trajectory shortens weakening the approaches. It's been a while since I've had to respect Link's play-style, but with Speed I can disregard a lot of things, despite being against a character who can zone while walling off with aerials & projectiles making it hard for Shulk.
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Jump
Lucario's ability to camp with Aura Sphere, plus Lucario's ground game feeling improved in Sm4sh, with tilts relatively the same besides Utilt getting KO power & being a lot faster, includes his AB%. One thing to not do against Lucario is use Buster Art unless you know what you're doing, & the Lucario doesn't. The main reasons why Jump is preferred vs Lucario is the Aura augmented to his ExtrememSpeed recovery, reaching very long distances being impossible to reach without using Jump's air speed & jump height to edge-guard & proceed chasing Lucario down while he recovers. Other minor reasons is Lucario being mid-heavy-weight, & his nerfed air-game unable to challenge you too much.
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Speed
Luigi still has strong air-game that can combo like a beast if you let him. Getting tweaks to several of his moves with a few buffs note-worthy, overall appearing the same. Doing less damage on moves like his D-air & his Fire Jump Punch UpB, his KO power feels weaker, but again still combo's like nobody's business, with good air-game & decent ground game. Shooting petty fireballs & Luigi Cyclone are the main specials he'll use for any ground game to approach with, so shield all that or vision counter the fireballs as he approaches towards you behind his fire. Same can be done for a aggressive Cyclone coming your way. Green Missile is esepcially counterable. Outplay Weegee with speed getting grabs off his landing aerails such as N-air, & you're good to go.
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Jump / Buster
He still combo's with Dthrow into Utilts, into USmash or Uairs, landing with Nair. Fireballs are still annoying, Cape & FLUDD gimp extremely hard without Mario trying too hard to rack up %. It's your pick between Jump or Buster, I'd prefer Jump to prevent the gimps by Cape & FLUDD's water push-back, that's what the amazing air speed from Jump is for. Never underestimate FLUDD & if you see it coming your way off-stage, always Vision counter it since you can counter push-back properties. Doing either Counter result will be fine AFAIK. Space some, shield fireballs, & avoid being gimped at all costs. Jump will serve you well.
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Buster
Since Marth's range is shortened, several of his attacks do less damage than they did in Brawl, & all of his throws have high knock-back at an early %, his own throws prevent himself to follow up with anything. Shulk's given range plus extra % damage output bodes well for both swordsman as Marth's counter is much stronger this game, yet the same can be said for Shulk's Vision counter when Marth goes for Shield Breakers to fish for a popping shield, mixed with large knock-back. It comes down to who outspaces who.
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Buster
Being a borderline mid-light character to me, MK gets some reasonable nerfs that are accompanied by several buffs to note, including his larger character size with more reach on his sword attacks possibly. All of MK's specials have been buffed in terms of strength & damage. MK's FSmash & USmash improved becoming stronger, while his Bthrow is stronger that deals more % as well. Though Shuttle Loop doesn't have much KO potential, it is compensated with better damage. Still an aerial fighter, it's best to go with Buster on this one to deal tons of % damage to his light-weight & bigger size.
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Jump
Ness' F-air nerf makes it underused now that it won't be his go-to aerial unless he wants to be close approaching with it. PK Fire being used at further distances doesn't bode well, while PK Thunder's shocktrail hit-box enlarged that also travels faster too. Shulk has no projectiles Ness can absorb with PSI Magnet unless the beam portion of the Monado counts as a Energy-based attack, which would suck very much for us. Ness got more buffs for his ground-game, but not too much buffs for his air-game, making him well-balanced on the ground & in the air. Jump's air speed easily closes the distance & doesn't give Ness any room to setup PK Fire or PK Thunder shenanigans. PK Flash apparently travels slightly faster, but that's nothing a Vision counter can't handle. Be aggressive towards Ness in the air & always edge-guard with Jump rendering Ness' recovery useless.
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Speed
Speed is the go-to Art here for the sole reason to stick beside Olimar most of the time & not letting him get space. When he throws pikmin, they reach farther distances & do more damage(?) but can only has 3 pikmin out at a time, being a major tweak to his metagame. His new UpB called Winged Pikmin, recovers based off the current amount of Pikmin held, so if you have none, you soar higher, while if you have 3 depending on the pikmin's weight values, would weight down the Winged Pikmin making it less effective. Speed keeps the pressure on him, & if Olimar can't keep a fair distance from you, he can't zone you.
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Buster. Peach's buffs puts her in a good spot. Her turnips got nerfed
, her Parasol & Peach Bomber both got bufffed compensated wonderfully now that Peach Bomber can hit Shields, but does less % damage. Parasol can stage-spike characters who are ledge-hanging, not to mention Parasol gets a KO potential buff. All of her tilts became weaker, now lacking KO power too, however they all traded off power & % with combo ability, making Peach's tilts combotilts with her better D-throw grab setups. Her air speed & running speed increased, though her F-air being the slowest aerial, is also her most powerful aerial. Buster with Vision counters for her Turnips if she tries approaching with them, along with Peach Bomber being easily countered. Peach isn't exactly a light-weight anymore, since she's considered middle-weight, but stick with Buster & keep your distance from her, she can combo like no other off her tilts & grabs. Several moves of hers got practically restored to Melee status, & that's never good for Shulk.
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Buster
I feel this MU will be decently in Shulk's favor, all that's really needed to be done is Vision countering ThunderJolts coming your way if Pikachu happens to be approaching with them, hitting him in the face for it. Vision proc'd for Thunder & Skull Bash prevents Pikachu from pressuring your shield. Avoid getting grabbed early as Uthrow to a couple of U-tilts to U-airs to a finishing N-air, the lower knock-back of the U-tilts & U-airs increases the string potential due to their lower knockback scaling. Pikachu has some nice buffed aerials like F-air being more powerful, so watch out.
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Buster
They play the same, but Dark Pit is stronger & doesn't scale as well with knock-back. Both have identical specials & for the most part, & almost the same move-set. Dark Pit has a few game-play differences, but they're practically the same MU. Their new UpperArmDash have super frames somewhere in their dash, so be wary when shield+grabbing or punishing with Vision Counter against it grounded or airborne. Make sure to avoid unnecessary pew pew arrows, & keep racking it up.
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Shield
ROB this time around got so buffed, his heavy-weight set & larger hurtbox gives his moves additional range, which in turn is a setback in favor for us, hitting him just got easier. All of his smash attacks got buffed for the better, Arm Rotor got a finisher that deals strong knock-back, & an improved yet nerfed Laser, including a mixed buffed nerfed Gyro. The Laser's full charge is a huge meaty Laser attack making you shield it, while the Gyro is quicker to charge, but less base % damage. Especially when Glide Tossing was removed from Sm4sh, ROB is hurt without it. Shield the lasers, the gyro, be wary of his Arm Rotor, & especially of his Smash attacks, most of all his USmash. U-air is multi-hit but now with a finisher at the end reliably KO'ing. Get in, & stay in mid-range with caution.
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Speed /
Buster
I can't stress enough how much I admire Samus & Link improving this much in Sm4sh!
Samus is a lot better & there's plenty of reasons. One her Z-air not only is a two-hit grab aerial, but has reduced landing lag & recovers quite well for a tether. Her CHarge Shot "drastically improved", & her missiles don't take long to reach max speed, with the drawback that firing missiles near the ground have landing lag, while her bombs don't stall her falling speed as much. As if that wasn't bad enough, her Smashes all practically improved with either more knockback, or more % damage, & her already good D-tilt now has even more KO power. Honestly, you either shield the projectiles, destroy them with tilts or aerials due to projectiles being generally weaker, or if you're close enough, Vision countering wisely can land a solid punish. Did I mention she's Heavy weight now?
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Buster
Sheik gets two new moves replacing her Chain & transform, now with Burst Grenade, & Bouncing Fish. Her needle storm no longer causes landing lag, her FSmash improves, & all of her aerials seem to of gotten a buff of whatever kind, be it more knock-back and / or more % damage. Avoid needle chips with shielding then rolling, or jumping. Sheik's may use Burst Grenade to wall you off, which in this case it's about near her area, so position yourself to be close to the blast radius in order to time your perfect Vision counter RIGHT when you notice being pulled in by the vortex effect. When you see yourself moving, instantly Vision counter to proc the pull-back property, & not the detonation itself. Bouncing Fish can be used as a mix-up option when Sheik's ledge-jump on the stage, so either roll away, shield it & wait for her to land, or use an anti-air U-tilt to stop her approach.
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Jump & Speed. You'll need these two Arts to keep up with Sanic. Speed only helps you match Sonic's movement speed, as you two zip across the stage mind-gaming each other. Dash pivoted F-tilts or pivot grabs are for throwing out attacks to space up some sort of wall. When your Speed expires, switch to Jump to combat Sonic with superior air speed versus his movement speed. This match may take a while but be patient. You'll feel it soon enough. Sonic's that get you off-stage while you're in Speed mode is risky due to Speed hindering your jump height, in which case Jump activated mid-way to recover more safely is suggested. Right as you get Sonic off-stage with Jump on, edge-guard him aggressively.
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Speed
Toon Link's buffed Z-air clearly makes his zoning & walling with chain a threat. To add onto that, his arrows take less time charging & travel further distances, along with his boomerang also traveling further as well. Bombs serve an extra purpose being another projectile to watch out for, but don't mind them too much when you can just shield, or VIsion when your nearby TL for a linear-dash punish. Really it's about getting close & staying close preventing TL from outspacing you, even though he'll attempt to space SH Z-airs keeping you out. Dash in & powershield grab if needed, & if that doesn't do it, then be ready to SH N-air all his projectiles & approach him carefully. Last thing to note is his D-air no longer bounces off us, he plummets straight down regardless.
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Buster
Wario being a heavy-weight & some different changes made to some of his moves, Wario still remains dangerous. With sped up tilts, less endling lag on DSmash, & replacing his old USmash with a similar one like the one Mario, Luigi, & Dr. Mario all have. FSmash has more range than before, though the main setback for Wario is unable to break his Bike into tire pieces. Automatically nerfing his item-play, even then, Wario still has his merits. His aerial mobility + your lack of knockback during Buster mode, may or may not mix well. Just be wary of his stronger ground-game, & be aware of his wacky movement. N-airs will keep him out, & if he charges with Bike we Vision counter, simple as that.
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Speed
Yoshi's most notable buff may be his Tail-based attacks reach increased due to it growing larger. Bair Uair & all of his tilts become more reliable thanks to that. Being a heavy character, Yoshi using his Super Armor frames in his DJ can make Yoshi into a revenge-dealing-fighting-dragonosaur. Jab1 can be canceled & lead into USmash if desired, & B-air has a finisher tail attack that can KO while edge-guarding. D-air used on grounded opponents horizontally launches them away when the ending finisher of Flutter kick hits, making the move safe to use landing. Jumping OOS returns to Yoshi at last. When fighting Yoshi, do not use Buster mode early game until you racked up enough % to deal fairly decent knockback preventing Yoshi from using DJ revenge Nair. Yoshi can super armor through a lot of moves besides Heavy hitting Smash attacks or tilts, so be aware.
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Buster
Her new DownB Phantom Slash is an easy Vision counter, proc'ing to do a linear-dash slash attack punishing Zelda for it. Her Dins Fire is also something to shield & move forward, be careful of it. Her F-tilt & D-tilt got buffed, D-tilt having less ending lag while reaching out farther distance. N-air & D-air also got buffed, D-air's horizontal range increased having additional % damage for sweet-spotting. Her USmash getting buffed & her Nayru's Love sped up basically means her ground-game is fairly good, so challenge it with Buster mode & blast her away due to her being a light-weight despite being border line middle-weight.
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Buster
ZSS being a Light-weight, Buster's setback of knockback bodes well to adjust for this MU. Except now she wears Jet boots, which apparently buff all of her kicking attacks.
Her whip reaches a bit longer this time, gaining a new Z-air, kind of like Link or Samus' Z-air, not good for us.
Her UpB Boost Kick does good % damage & has good KO potential as a combo finisher, meanwhile her FSmash deals more %, & is stronger. Lastly, her Paralyzer & Plasma Whip all zone out Shulk preventing any approaches, along with Flip Jump now able to bury opponents. Running Shield canceling Paralyzer shots to prevent unneeded % damage & paralyzation, while also avoiding DSmash too. Play smart, don't be hasty, & land Vision counters to punish ZSS paralyze shooting or Plasma Whipping.
But enough adulting, the damage perk does make up for the 2 setbacks built-in to Buster. I'm content if Buster has no combos early game, because frankly the reduced launch power setback essentially reduces hit-stun, so there won't be true combos until maybe after 20%-ish. Even then that's almost achievable from just grabbing > pummel x1 > B-throw, which we've said already is huuuuuuuge. 
