ult
mechanics
air
compared to most other fighting games, smash bros is incredibly air based, with aerials in at least ultiamte, the newest smash bros, being the only practical way to play neutral in most scenarioes
in smash bros, characters move around a lot, and most ground normals are relatively stationary, unless combined with momentum, like from a wavedash or a pivot depending on game.
this makes spacing them kinda hard and restricts how they can be used. also, they only have limited vertical utility, which makes using them against airborne opponents not as easy as aerials.
additionally, characters have a lot of in air control, and they maintain most of that control even during attacks.
an example: you are spacing a small attack on block. most attacks in smash bros are unsafe on block, and nearly all block pressure is a mixup. you want to be safe, but its so small you cant space far enough away to be safe, what do you do? you drift backwards during the recovery frames, so that you land further away from the opponent!
this kinda in air control is in contrast to a lot of fighting games which have extremely stiff and telegraphed jumps and in air movement in comparison. some fighting games dont even give you access to any momentum or location mixups in the air, or even the ability to do a defensive option!
block pressure
block pressure, as it is in most fighting games, doesn't really exist in smash bros, or, at least some of the games.
true block strings are essentially non existent outside of a few niche scenarioes, if we exclude the first smash bros game, where getting hit while pressing shield essentially meant you lost that stock.
smash bros also doesn't have dedicated high low mix in nearly all circumstances (even if someone's shield health is low, i've only ever seen one person ever actually go for a high low mixup), doesn't have the same kind of on-block cross ups, and also doesn't let you block forever.
shields block everything at all times unless it is something that is unblockable, like a throw. even moves specifically designed to deplete all of a shield's health can be blocked, if you have enough shield health (which, competitively, only comes up when shulk is in shield mode). when shields run out of health, they shatter, or pop like a bubble. having your shield broken is essentially guranteed stock loss. It Sucks.
in that sense, true blockstrings could be extremely silly in smash bros, as is. attacks do far do much shield damage where if you could reliably link into each other, you could just use a relatively safe move on block, and then hit confirm it into something else to pop shield and cash out your earned stock. in fact, the few situations where this is possible, this is what actually happens most of the time, unless the player gets hit by one of the moves through the shield.
in smash bros, this often happens when a strong projectile, especially one that can be followed behind, hits shield. projectiles only cause hitlag on the person being hit, not the person who sent the projectile, so you get dispraportionately large amounts of advantage frames when doing this. in smash 4 wii u, samus could launch a missile, and then wait for it to connecct, then whip out a full charge charge shot to get a true block string that instantly breaks shield. lots of characters in ultimate can do this, and it was so good that there was an entire balance patch in the first couple months of the game's life that was specifically about weakening the shield damage of projectiles.
all other examples are either explicitly meant to be true blockstrings, like rapid jabs in smash ultimate and multi hitting moves specifcally designed to break shield, like DK hand slap, or are extremely niche, like fox multishining on someone's shield until either the shield pops or the fox can't keep it going anymore.
something incredibly silly about true blockstrings in smash ultimate is that in a lot of cases you can just get a free throw in. You can be grabbed during hitstun and blockstun in smash bros., meaning that even if a true block string doesn't just outright kill someone, it would still give their opponent a free opening. Sometimes we'll see mii gunners in smash ultimate lay a timed bomb at ledge for corner pressure, and then flowchart grab someone if they block the bomb, and its a guranteed grab once youre in blockstun
when shields lose health, they become physically smaller, and this means that they become less effective tools for blocking. smash bros lets players angle their shield in any direction, and this is useful when your shield health is relatively low. when shield health is low enough and someone is good enough at spacing, you can introduce traditional fighter high low and block cross ups. although, smash bros isnt streamlined with it, there aren't dedicated highs, and there isnt like a guranteed way of knowing if soemthing will work on cross up. it is just, if you hit the exposed part of the character, and not the shield, you land the hit, but if any part of the move connects with the shield bubble, you hit the shield.
some moves, like marth down tilt, are specifcally designed to be used as lows, and in some games that is how it is often used, as well as a general poke in neutral. highs are really uncommon and only occur in very weird scenarioes. when we played roy, we sometimes used last frame of weak up air to hit people's block high, which then at high percents lets us convert into a kill. it's pretty good at being a high if you know how to use it, since there is basically not chance it will hit the shield unless someone is specifcally blocking high.
cross up's only really exxist in technicality. since ambiguous cross ups can't really exist since they would still hit the shield, you'd need some unreactable burst of speed or something to space yourself far enough behind someone.
in smash bros, cross up usually has a different meaning. in traditional fighting games, a cross up is when you hit someone blocking by hitting them from behind them, where they arent blocking (although the opponent can always change their blocking direction, but this is easier said than done.). in smash bros, cross ups happen when someone attacks a player's shield, and then end up behind the character shielding. This is different from regular cross ups, since the opponent never actually gets hit by the cross up attack, and instead, what they do after blocking changes.
An ambiguous cross up in smash is when its hard to tell which side of you your opponent will be on after an attack. In smash ultimate, there are a load of ground moves and special that are ambiguous, mainly because of collision box not working consistently across the cast (in ult, youre not supposed to be able to go through an opponent while grounded, but some ground moves let you sometimes do it anyways, and soemtimes dont let you). in all smash bros games, aerials, when combined with drift, can basically all be ambiguous crossups. Imagine if you got hit for not blocking a cross up in smash bros.... oh, that's dragon ball fitherz.
in smash bros, some matchups are just safer to play by doing crossups, whereas some of them it is just a mixup. in older smash games as well, cross ups were very important for safety since it completely nulified grab out of shield as a punish on point blank attacks.
in smash bros., characters can cancel blocking into a couple of different actions. they can cancel it into an invulnerable roll or spotdodge, or a jump, or grab. In smash bros, you can cancel pre-jump into a up smash or grounded up special, so that you can still use those moves without jumping. this means that jumping out also lets you use those two moves.
having good up special out of shield lets you change your facing direction when coming out of shield, too, since special moves let you change their facing direction during startup. in smash ultimate, cloud, from final fantasy, who uses up special to gurantee punish unsafe things on block, does not particularly care about reactable cross ups, because they can just turn their up special around to hit the person behind them. in this matchup, the goal is mainly to make the cloud not able to react which side you land on, and choose the wrong up special direction, so you can get a punish, and then to use that to make them second guess using it out of shield again, even when you dont cross up. or well, at least in theory.
you can do something similar against characters with strong up specials and to a lesser extent up smashes out of shield by feinting an aerial but instead landing with an airdodge or shield so that you dont get hit by the option. a lot of the time this is just a vibes and knowledge check, if someone is anxious or just doesnt know that they can hitconfirm off of shield stun to know they will get a guranteed punish. at high level, we mostly see stuff like this come up with tick throws, which aren't reactable. jab someone's block so that they do an upspecial to stuff out the grab, but then you shield it cuz jab doesn't have a lot of endlag, etc..
because of the fact that nearly any attack is unsafe on block in smash if it isn't spaced, it really changes how blocking is played compared to other fighters. block pressure doesn't really exist in smash bros.. in smash ultimat ea few characters like terry and sheik and ken do have legitmate shield pressure because they have unreactable on block buttons that also combo into big damage or kills. for example, sheik jab, LMAO. sheik jabs your shield and its like okay yeah i could punish this but like its so fast that no not really but if i try and challenge it their frame 2 jab will beat out literally any option i have unless i have like fucking fox shine or something and the thing is sheik never HAS to press jab she could just stand there and try to get a down tilt or reset by jumping and forward airing which is by the way extremely safe on block and literally unpunishable by anything if done perfectly and not parried. also jab kill confirms
most of the time, shield pressure in smash bros is more of a "what are you gonna do next" kinda thing. izaw smash's video on smash wii u ike has a pretty good example of this. it's very different from other fighting games. we'd argue that smash bros' advnatage and disadvantage state during punish are much more similar to traditional block pressure than smash's actual block pressure is to traditioanl block pressure. blocking in smash bros is signficantly more of a neutral tool. for example, if your opponent is spacing and walling you out, you can intentionally over extend into their range, put up your shield, and then get them to hit your shield mis-spaced, cuz they didnt expect you to be point blank. then, you can punish them, or you can reset to neutral but now much more heavily in your favour. this partially works cuz basically everything in smash is unsafe when not spaced, at least to some extent.
in smash bros games after brawl there is a very funny out of shield option that involves jumping on your opponents head. which has HITSTUN. it does zero damage and also propels you away from your opponent meaning that even though you are frame advantage you are still putting yourself into disadvantage because of how strong the upwards momentum is. unless you have a way of getting back down to the ground, or just a silly large hitbox.
never seen someone use this in brawl. if brawl has double jump cancel then i imagine like fucming yoshi would use it. all i can think of is meta knight footstool tornado. maybe it doesnt happen cuz of shield pushback and difficulty of forcing a misspace. in smash wii u, mewtwo players used this a lot to connect disable, which was otherwise impossible to land in a match (it wasnt a projectile in wii u; it was a point blank move only). this works because mewtwo's specials all interact with their momentum in unique ways. up special carries a lot of momentum, side special cancels your vertical momentum but maintains your sideways momentum, shadow ball cancels both while unless at the peak of your double jump, and disable cancels both.
mewtwo would footstool the opponent, then double jump to the correct side of the opponent (disable is facing direction dependant), and then cancel double jump with disable, and stun the opponent. Also mewtwo used footstool disable in an infinite LMAO
i know marth an lucina can do foostool dair on some characters. i think this doesn't work in ultimate because characters have sigfnciatnyl faster upwards acceleration that makes it so youre too far away by the time the hitbox comes out`
this is a lot more well known in smash ultimate and a lot more people and characters go for it. it is universal frame 4 out of shield option and some characters, like, *ahem*, mewtwo, get really nasty shit out of it. like, you know how it gave mewtwo an infinite in smash 4? that was removed in ultimate but like they are just so fucking glass cannon it wouldve never even mattered cuz youre just taking longer to do something you couldve done ages ago. its really good. only works on air moves