Was unable to post my full thoughts earlier due to work.
Top Tier:
I really don't think this character has any sort of true weakness. Sure, she might be lighter than a good portion of the cast, though this only helps her escape combos more than anything else. Several disjointed hitboxes, strong attacks, two recovery options, incredible speed, great Dthrow for combos, great projectile for combos, incredibly low landing lag, an Up B that kills and is a great OoS option, Zair for zoning, and more. Seriously, what was Nintendo thinking when making this character? Unless she is patched, there is no way this character is dropping down to anything below top tier.
Very similar to ZSS in that she has no true weaknesses...kind of. Unlike ZSS however, she does have a few weaknesses, but they are backed up with even more insane strengths. She's extremely light and a huge target, making her easy to send far...were it not for the fact that Lumas protect her pretty much 24/7. Easily the best trap/stage control character in the game with how Luma works, and this strength is further amplified by how her normal moveset by itself is above average as well. The only thing it really lacks is KO potential, which Luma also covers. And losing a Luma hardly matters due to how quickly they respawn. That's honestly the biggest complaint I have with her. If her Luma took longer to respawn, she would be a lot more balanced overall. Either way though, I can see this character's potential only continue to rise, especially since all of her custom moves are good as well. Oh, the fact that you can't really pummel her or grab her for long also is quite annoying as well.
The last of the "big three" of the strongest characters in the game, currently anyways. But these three don't appear to be going anywhere any time soon. She has one of the best projectiles in the entire game (needles), which are great for free damage and interrupting your opponent. She also probably has the best combo game out of the entire roster to boot, with how Ftilt/Dtilt pop opponents up for juggles, Fair has literally no langing lag at all, her Bair/Nair also have very low landing lag, her throws are great for setting up combos/strings (especially Dthrow), and more. Bouncing Fish is an amazing special move that helps with KOing, recovery, and techchases to boot. I haven't experimented enough with her grenades though, so I am not too sure how good they are. Either way though, she is really fast and has no troubles at all being able to get up in your face and lay down the pressure. Her one minor flaw is that her KO potential is somewhat lacking besides Usmash and Bouncing Fish, though this hardly matters. The only other thing holding her back from being "God Tier" is that her recovery still leaves a little to be desired, even though it got buffed with Bouncing Fish.
Sonic got quite a few buffs, in all the places that he wanted to have them. More speed, more KOing power, a better Dsmash/Dash Attack/Homing Attack, more differences between Side B and Down B...and a metagame/game engine to better suit his playstyle. Because Smash 4 heavily relies on footsies, and with the addition of pivot tilts/Smashes to his arsenal, Sonic won big in this game. Not to mention, Side/Down B to jump to Nair is pretty much a free 30% damage combo against the opponent whenever you are able to hit them with it. He even still has Spinshotting still, and a new ability (which I somewhat discovered) called "Instant Spin Dash Jump"...which further adds more tools to his ability to approach and combo opponents. His Uthrow is also great in that he can chase the opponent afterwards using Spring, and then follow up with Uair. He still has a few small problems, he doesn't like being shielded against and his aerials have quite a lot of landing lag. But in regards to Sonic, this character has gained a lot of new ground, and is only going to continue to pick up speed.
Pretty much the character Mario always wanted to be. He's above average at pretty much mostly everything he does. Good recovery, good damage, good speed, good KO moves, good combos, good projectile/trap, good techchase with Side B, good throws, good gimping potential and a great meteor Dair. Overall he's just really solid, and there's not much else I can really say about him. He just simply works. Sure, bananas took a pretty hard hit, but everything else he has seems to have gotten better. He is also one of the few characters who has two throws which can lead into true combos (Uthrow and Dthrow). His main problems are that he has one of the
worst jabs in the entire game (just use Dtilt instead), and his Usmash tends to miss opponents more due the the last hit being a linear uppercut now. And...that's about it really. Simple, fun, and effective.
Probably the weakest of the top tiers, but still incredibly solid. He has a nigh-flawless combination of ground and air speed which feels exceptionally fluid, which is great for both approaching and retreating. Lots of coverage/pressure from eggs to keep opponents at bay, especially with Dtilt to help keep opponents off of him. Dtilt also helps him put the opponent into a position where he can gimp/spike them off of the stage too. His Utilt is great for following it up with Uair, Bair is great for playing both defensively and offensively and it can KO, and Dair just
destroys shields and spot-dodges. His new Usmash and Dash Attacks are great boons to his arsenal as well, but the loss of his old Usmash means that he is a bit more vulnerable from behind. His recovery is still a hindrance, and Egg Roll still pretty much sucks unfortunately. But other than that, he's really good this time around. And he's got a few good customs to boot, specifically his Star Egg custom which gives him yet another option to zone people out.
High Tier
Ness is pretty great in this game, though I feel as though he is being slightly overhyped. But that is just me. His ground game still sucks, his Dthrow -> Aerial combos drops more often than I would like it to, his Dair is worse in this game (much to my dismay), and his recovery is...well, still incredibly easy to gimp. Fair and PK Fire are still great for keeping people at bay, and his Dsmash YoYo feels better in this game too. And the fact that PK Thunder is actually a great projectile in this game is quite humerous to me. Even so though, I feel as though his potential might wane over time. What he does good at, he does pretty good at. But exploiting his flaws is like an Achilles Heel, and brings him to his knees. But for now, it's good to see him finally have some time in the spotlight. At the very least, he has Lucas's PK Thunder to help him with his recovery in this game, so that's something.
Probably the most buffed character in the entire cast, in my opinion. The sole fact that it
feels like I am playing Captain Falcon again and not a bottom tier character alone gives me a lot of hype. Utilt spike is just a brilliant buff that helps both with edgeguarding and combos and I love it. And his Knee of Justice actually KOs again now. Gentlemen is great in this game, Dtilt sets up for gimps, and dash grab is just
scary. His recovery is still bad, however, though Up B is good for racking up damage sometimes (17%). I did notice one problem however. If he uss his Up B and hits an opponent with it and then lands, he still has the Up B landing lag afterwards. Though this can be fixed by using a Uair before landing upon the ground, which has little to no landing lag and is a great move anyways. Overall though, I am thoughroughly impressed with Captain Falcon in this game, and "I'm glad he is back."
I feel as though people are overestimating this character, but not by too much. He has trouble killing, his tilts aren't too spectacular, his smashes are kind of slow, and his Side B has too much startup and endlag to be useful despite how cool the concept is. But everything else he has is really good. Nair can chain into both Usmash and Fair at certain percents, his projectile is pretty good, his recovery is amazing, and his aerials are all really solid. He wants his opponents to be in the air as much as possible, since he pretty much out-Falcos Falco in the sky. He seems to have a bit of trouble when people get up in his face though, which is why I feel as though people are giving him a bit too much credit. But otherwise, he is a really good character.
People should not underestimate Marth's strength. Tippers are very scary. That being said, his recovery still sucks. Being able to easily kill at like 80% is no joke in Smash 4 though.
Mid Tier
Currently a little overhyped right now, at least with default moves anyways. He is incredibly threatening if he hits you however, but he is still susceptible to combos and being zoned out. With his Dash Grab custom however? Definitely ends up being a high tier with that move alone, as it increases his mobility and gives him a techchase that he can easily abuse. I can only see this character's potential grow over time, at least accounting for the high probability that customs will be allowed.
A great mindgame character with Side B and Mechakoopas, but falls a little flat in being great due to his inability to KO at reliable percents. I think one thing that people are overlooking is his ability to mitigate damage/combos due to his unique mechanics, though most combos will still probably hit him anyways since he is a fatty (and can also take more damage instead, also due to his unique mechanics). Side B also isn't as good as people think it is, since it is rather easy to block with good prediction. Even so though, like Bowser, I can only see this character's potential rise, also accounting for customs probably being allowed in the future. Giant Mechakoopas and his Spinout Side B custom being prime candidates for helping him shoot up in regards to competitive viability. (Also, his cannonball move sucks imo, and none of his customs help with that)
Very similar gameplan to Bowser, but a tad bit more agile and less strong. His 10-Wind Giant Punch is no joke, and can KO opponents at around 50% or less depending on the situations. I also really love his new Down B spike in the air now, which is probably his best spike besides Dair (also having 4 spikes is pretty awesome, even though the Side B spike sucks in this game). Other than that, DK feels like DK in this game, and is overall pretty solid. Like Diddy, he is very simple and straightforward.
Not as bad as some people say he is. Dthrow and sourspot Nair are still great for combos, and I still love how his Jab 2 can set the opponent up for being grabbed afterwards. His Gordo can be punished, but it still needs to be respected as well. I also think that people should use his Down B more, since it has quite a bit of knockback to it. Either way though, his weaknesses still definitely hinder him though. His speed doesn't do him any favors in particular, and it's not really fun to have a Gordo come back and smack you in the face. DeDeDe still definitely works though, and just requires more patience to play as in contrast to a lot of other characters. His Dash Attack is still absolutely horrendous, however.
Definitely not bottom tier, unlike how quite a few people think he is. None of his toolkit really flows together, though this makes Mega Man also quite unpredictable to fight against. Reflectors are his bane, but otherwise his zoning potential is not to be underestimated. And depending on who he is fighting, he could end up being really great or...not especially great, but still fairly decent. Also, Leaf Shield isn't bad. It leaves a lot to be desired, but it still has definitive uses and situations in which it can shine in.
The sole fact that she can't KO as early as Marth drops her down a tier. I tested her hitlag on shield in comparison to Marth and didn't find much of a noticeable difference. Even so, she's still pretty solid with both things considered. Just not as good as Marth, and no real reason to use her as opposed to Marth...unless you really like the character or are looking for a challenge.
Low Tier
I don't think Luigi is as bad as people say he is. He's not great, but not incredibly bad. His Fireballs are good for zoning, his Down B is decent for techchases, he has the easiest Dthrow to combo after in the world, and his recovery is pretty decent. He also has quite a few custom moves to help add to his viability as well. In particular, I found that his Floating Missile custom helps quite a bit with his ability to edgeguard, with its increased knockback and decreased charge time in comparison to the standard Green Missile. His low air speed and inability to reliably KO are still huge pains in the neck though, as well as his short range. He can still win though, but he really has to earn it. You have to be very patient with him (like DeDeDe), as Luigi seems to be more of a defensive character overall. Also, be careful of his bad traction, too.
Would be MUCH better if every single one of his moves didn't lag so much. At least his Nair and Monado Arts are fun though, and he has a ton of range. But I doubt he'll end up any higher than this. He also has the worst Jab in the game, along with Meta Knight and Diddy, which is rather unfortunate. Speed Monado -> Buster Monado -> Smash Monado seems to be his best gameplan in a match, with Jump being used for Monado landing lag canceling and Shield being used in desperate situations.
Bottom Tier
As much as it pains me to say it, but I really don't think Mario is all that good in this game. With customs he's a lot better, but his default moveset is quite bad. He might end up in lower tier with his brother Luigi, but I am not so sure at the moment. He has to read his opponents nearly twice as much as any other character has to, because of his low damage output. He also has a lot of trouble KOing too, having no good aerials to help seal a KO for him. He has pretty good speed and little landing lag on Nair/Bair/Dair, but that's about it really. His short range, slow fireball, inability to KO, lack of damage output, surprising difficulty with certain combos, incredibly poor recovery, and other problems just pile up too much for him to handle in some matches. In Smash 4, Mario takes "Jack of all trades, Master of None" a little too seriously. With emphasis on the "Master of None" section in particular. It feels as though everything he can do, another character can do better. He can still win matchups, due to how balanced Smash 4 is overall, but most battles are going to be uphill ones for him. Or at least, even at best. FLUDD was buffed, but its potency is a bit lacking due to how a lot of characters can easily recover in Smash 4, and with how moves tends to send opponents at higher angles in this game. And while Explosion Punch really helps solve Mario's KOing problem, it makes his recovery worse and takes away some of his combo options. The one thing he has with no drawbacks is the Gust Cape, which helps both his recovery and is amazing for gimping potential. It will only take him so far though, as every other character has access to equally amazing custom moves too. In short, Mario can still win against most of the cast, and I might be being a little too harsh on him. However, as a Mario main for 10+ years, I can say with absolute confidence that he is below average in almost every category. I am still very dedicated to the character and I will still always play as him, but I feel as though winning with him will be a struggle due to his drawbacks as opposed to my skill as the player (most of the time). And that's the kind of feeling that you should never really feel when playing a character in a fighting game, barring joke characters.
Pretty much the same as above, only noticeably much slower but with a little bit more KOing power. One-Two Punch is the absolute worst recovery in the game, even worse than Little Mac,
and that is absolutely horrible. On the bright side, one of his Down B customs helps with his recovery. Since you pretty much won't be using Down B to attack with much anyways, and Doc needs all the help he can get in regards to recovery and mobility.
Why on Earth did they think giving this character more startup lag on everything was a good idea? I seriously think that Kirby needs to steal some of ZSS's overall speed, and then both of them would end up being more balanced characters. I also dislike how Stone is nigh-useless now that you can't really cancel out of it super early as before. He's not Melee Kirby bad, and he can still win like Mario, but he is definitely below average in comparison to the rest of the cast just like Mario. I miss his 64 days...
Would be a lot better...if they didn't nerf his weight to hell. He has potential, but he won't ever truly shine since he pretty much gets swatted away like a gnat. Just because his new Up B is a pretty decent recovery, doesn't mean he should be this light. Heck, Villager's recovery is extremely similar, and yet he's almost as fat as Mario. I seriously don't understand Sakurai balancing sometimes. :/
Cheese Tier
Along with Mega Man, though to a much higher degree, he is the most polarizing character in the entire game. Depending on the matchup and stage, he can either be extremely good or extremely bad. Which I personally find hilarious, since it allows him to be very serious...yet chock-full of laughs due to how easily he gets wrecked in certain situations. So while he might not be the best or worst character in the game, he is certainly unique, and very fun to play and play against. Super armor on Smashes is a bit too cheesy sometimes, but you simply cannot have Mac without the Cheese. It is an unwritten rule that should never be broken.
Not Sure Yet