a couple thoughts i've been having about various matchups:
vs
: i usually hold A to jab away the stun blaster. a lot of zss's will dash in right after and it's often a 50/50 whether they'll go for the dash grab which you can easily spotdodge and punish, (or continue to hold A to get them with the jab combo if they space it incorrectly) or go for the dash attack, which is a little harder to spotdodge because of the timing but you can
sometimes catch them out of this by continuing to jab. good zss's will mix it up by either down B'ing or using aerials, in which case, you don't want to be caught holding A at all. also, zss's down B is incredibly telegraphed -- if you're expecting it, you can easily upsmash/upB them (jc OoS works) and KO early. zss likes to recover using down B esp when they're just out of reach of the ledge, so look out for it, and if you read it you can punish easy.
vs
: you can nair out of ftilt combos at low percents. won't necessarily give you a frame advantage, but may screw the opponent up and reset the neutral. you can also upB out of it, but it's obv more risky. just like zss's flip, you can/should punish bouncing fish with upsmash or upB (jc OoS works) -- you should feel for when the opponent likes to use it (often recovering by the ledge, do
not try to dsmash her recovery). also note that at low percents, if you hold up+in when you're being f-thrown, the bouncing fish combo should not connect. also, bouncing fish is
not as fast as it feels -- if you spotdodge it, it's a free punish (but sheik recovers quickly so decide fast). otherwise, don't get faired. if you do, don't waste your double jump or you're dead.
vs
: if you can superarmor his nair, go for it. the main problem is the gyro+laser combo because it forces you to approach, applies shield pressure, and zones you out. try not to shield the gyro, as the ROB can just make another one right after it disappears. what i like to try to do is grab the gyro and throw it up (jc glide toss for movement or whatever). this keeps the gyro in play and makes it 'mac's item' (i.e. it will hit ROB instead of mac). also gives misdirection and you may be able to get a hit or two in before the gyro lands, where you can try to pick it up again and reset by throwing up. as long as the item is 'yours' ROB can't throw another gyro, so you can just read the laser attacks, which can't be done continuously. i think the space between lasers is 4 seconds -- any sooner and nothing will come out. also, don't roll around ROB predictably, because ROB's dsmash lasts long and covers a large area so you will likely get hit by it and perhaps get uaired after. ROB likes uair as a kill move because it lasts long and has good kb at higher percents (beep boop combo or whatever it's called), so try to watch out for getting grabbed.
vs
: i find that mario and sometimes luigi is weak to 'wavedash-like pivot fsmashes'. usually mario's regular approaches are nair, bair, dash attack, spin tornado, and fireball. if they're approaching by any of the first four options, right before the attack connects you can run back like _one_ step and pivot fsmash punish every one of those approaches with your superarmour. (side note: sometimes this works against sheik's nair/fair approaches, but it's a little more unsafe because sheik). for the fireball approach you can't do that, and usually mario will come in for the grab because your instinct is to shield it. read the fireball. if they fullhop/short-hop the fireball you can often run underneath and upsmash as there's a surprising amount of lag on mario's neutralB if you get past the fireball. if they throw the fireball and start running right after, you could jab the fireball away and continue to jab to catch their grab attempt. sometimes, they will mix it up by rolling behind you to grab you, so look out for that and spotdodge. also watch out for when mario lands with an aerial nair/bair, because it autocancels and he will almost always follow with his jab combo which is deceptively fast. don't get caught by that. EDIT: i forgot to mention, if mac's counter frames are active before he gets hit by the FLUDD, he won't get pushed back. situational, because if you get read you're screwed, but good to know if you get the read.
vs
: luma can't shield (spotdodge?), so you can usually get rid of it with a DA, ftilt, fsmash -- anything the opponent would usually shield. also, when rosa has to recover from far with her upB, there's no hitbox, so if she's going for the ledge feel free to run off and jolt haymaker back towards the stage to stuff her recovery and add damage, possibly stage spike. i forgot you could probably do this to ROB too, but it's a little more risky as ROB can read that and sometimes act out of his upB to mess you up.
generally, i've actually been trying to implement this run-off-sideB-to-ledge ever since i saw that combo vid in the video thread. when it's not expected, at worst you get a ledge trump which you can punish on regrab with a dsmash or read. at best you get an unteched stage spike. anyway, anyone have any other thoughts about these MUs? if i'm wrong about anything lmk, but i thought this kind of discussion might be useful.