1. what attacks can reliably thwart squirtle's armor? i found out d-tilt doesn't work until like 63-ish... how viable is it to grab his side B?
Grabbing side-b is very viable. You can flaw it if they do a kind of dashdance with it but if you forced them into it you can f-smash%grab gamble with clear advantage on even read distribution.
2. what moves of sonic do you need to watch out for in neutral? like, what are his best pokes, fastest moves, shield traps, and anti-CC moves, etc? also, something i want to ask about specifically is his anti-airs vs you, especially vs your nair and fair zoning. i always try to play a very grounded marth, but furthermore, i don't really know my limits as well in pm vs melee, so i find myself getting punished in situations where i think i'm safe bc of melee.
All kinds of SHFFL aerials, but thats the same against most characters. Down-b and side-b are the most Sonic specific neutral game things. Sonic mostly works with fakeouts because he can't rely on his grab only and you can shield most other stuff. Grab is anti CC obviously, but fair, nair and up-tilt are also depending on percentage. Only try CC when he spins normally because his side-b kick and his down-b are fairly weak to CC. Airwise his nair has some combo breaker properties and dair can trap you when you want to air chase him with up-airs. He also has better landing than other characters. Also he has some escapes with up-b, beware of the spring projectile. Summed up, if your reads are decent you will have a slight neutral game advantage, be a bit cautious with overextending in the air and crouch cancel/shield his spin stuff.
3. how is marth's throw game different between PM and melee? i've generally been trying to just get whatever guaranteed uthrow combos i can and then trying to play the positioning game from there on to eventually find another hit, but i don't know if marth's side throws have some new hotness in PM or anything lol.... or if marth's ground traps are (relatively) stronger in PM just because a lot of the new characters have a lot more mechanics to escape juggles.
Up-throw stuff generally works, best followup being up-tilt (against the mass of the medium fastfallingness). Do f-throw more than usual against bad techrollers. Characters that are heavy and floaty have an easy time getting out of up-throw followups at mid %s (like Zard, ROB and maybe Wario), so then go for full mindgames / DI traps. Lighter floaties can be chased with full hop up air until higher mid %s, at high %s you won't get that much off a grab then. If you don't have anything guaranteed mixing up is mostly between f- and d-throw, and if you are barely out of up-throw followup percents you can also include up-throw (it seems less DI dependent, so if you clearly don't get anything with it, f- and d-throw are the better guess game moves.
4. wtf is going on with olimar? i don't understand what this character is doing at all nor who wins the MU.
Have no clear opinion on how the matchup is, probably around even. To explain the character, you need to consider basic facts first. He is easy to edgeguard, capitalize on that. His pikmins get stronger with time, don't let him camp. F-smash can mess his pikmins up because of different kb angles, also use it insread of other punishes even if it won't tipper. Olimar has great SHFFL aerials, don't just go fair spam. His grab is kind of slow, you want to grab him more instead. He has a great down smash, it may hit you out of grab or punishing you whiffing a grab or going for down-tilts. Thats the main struggle, you should go for grabs much but he will do the panic d-smash if you do it too much (you can easily punish if you see it, wait->grab, sh->nair/fair etc.). Nair is also good in that matchup because of the multiple hit interfering with his pikmins better than fair. Your grab game is pretty standard, mostly up-throws and mindgames at higher mid%s when it stops working guaranteed.
5. what's the run-down on diddy and his bananas? i recently played a diddy and i had no idea what i was doing with marth, so i had to cop out and go fox. i was respecting his bananas a lot, but after tinkering around with the character, i'm starting to think i need to apply a lot of pressure on him to not let him get any bananas out in the first place.
regardless, i will inevitably have to deal with his bananas at some point, so how do i do that? is the best course of action to catch them, shield them, WD over them (can you hit his bananas?)? and once you *are* holding onto a banana, how should you use it? throw it back at him, or just release it? in melee, marth's item throw was TERRRRRRIBLE, and i don't know if it is the same case in PM.
You need to pressure against Diddy Kong. If he doesn't get bananas out you have a fairly "normal" matchup. I will just discuss now what you should do if Diddy gets the bananas out. You are in a slightly worse matchup, but that means you can still do much. First, you can hit them away, but this will result in big frame disadvantages, not a thing you want normally. Catching them is a great choice and is possible by both press attack and WD. While Marths WD is great obviously, I find it to be more difficult to catch a thrown banana with a WD and would prefer a "normal catch then", if it lies on the ground WD is superior. If you have the banana you have many choices, I like mixing it up a bit but prefer "forward item throw"->grab for aggressive play and roll glide toss up (roll and c-stick up, probably the accurate name is an other one ^^). If they are not running in a nice perfect reflect shield also does its job. Sometimes you can also just crouch under the banana (mostly if they sh throw forward the banana) then this is a fairly good while not-commitive option. Also do mixups here, sadly there is no simple beating option but you will need mindgames but OK, thats how it is.
6. any notes about the offstage game vs MK? whenever i fight MK, i always feel like i break even or have a slight advantage in neutral, but i get heavily outpunished. i realized that i had a poor approach to comboing MK, which is why i'm trying to learn more about marth's throw followups in PM, but i also want to know about the offstage game. how good is marth's edgeguard on MK, and how good is MK's on marth?
Marths edgeguards on a MK are not that reliable. MK has shuttle loop and reverse shuttle loops, with different timings and different amounts of jumps burnt before. He can also try to sweetspot with jumps only. Try to gamble between read onstage recovery and read sweetspot recovery, f-smash and shield breaker are your main tools. I could specify more detailed later (short on time...). Grab followups are pretty good, I would prefer the up-throw ones because MK is a mid-fast faller (not quite spacie but over average)
7. also, i'm just curious..... what are marth's hardest matchups in PM? i want to use him as much as i can bc he's by-far my strongest character, but i get better mileage off my fox a lot of the time just bc you don't need as much matchup experience to thrive in PM with fox, but i know i'm going to have to put in work to overcome some new matchups, whether it's to polish my fox up or to tune my marth in to the new **** he has to deal with. i'm basically wondering if there are any characters where i'm straight up BETTER OFF learning a counterpick than i am trying to learn the MU.