Im not as experienced as the others, but the only thing that improved vs marth for me from melee was the 3.0 zair.
the 3.5 zair does nothing to help.
A minor help is the Fsmash extra range with the explosion. can help punish a whiffed tipper.
I don't think it actually has any extra range, in Melee the hitbox is stilll stupid disjointed. If it does, it's only a little bit extra.
Screw it let's make a matchup chart:
55-45 : Samus can pretty easily camp Bowser, and he's one of the few characters she can actually combo. Edgeguarding is stupid easy. However, she has a terrible grab to try and exploit is biggest weakness, and one wrong DI off of Koopa Claw or dash attack is probably a lost stock.
45-55 : Falcon might be even, but Falcon doesn't really have to try and Samus has to play super well.
60-40 : Neutral is a breeze, edgeguarding is easier now, can combo him cause he's fat. Charizard can kill her pretty easily off of vertical combos though, and she gets edgeguarded just as bad if not worse.
45-55 : Easy to combo, but you get punished every time you hit him below like 30% cause he suffers no hitstun and has insane range. He can edgeguard Samus really well, and is one of the few characters with better survivability than her.
60-40 : Combo-able, Samus has a good glide toss, Diddy can no longer kill. Without that stupid up-throw that killed her at like 120% last patch, this matchup is a lot easier.
65-35 : Probably Samus' best matchup, Kong doesn't get many followups on her, and can't deal with Missiles effectively.
50-50: Falco is still amazing and lasers will always be dumb. Crawl helps but only a little, good Falcos can shoot that low anyway. Samus should touch of death Falco if on point though.
45-55: I'd say this would be even or in Samus' favor with 3.0 tethers, now there's no reason not to die now if you get knocked too far off stage.
50-50 : Autocancel n-air is dumb, negates most of Ganon's projectile weakness. The cape means you can't just jam charge shots down his throat when he's off stage, and Ganon gets legitimate combos on Samus. If you have to tether, prepare to spend the next 30 second repeatedly being hit off stage, cause there's no way back. Gimping him should be easy, but playing around float makes things different. (Side note, when Samus does the forced tether jump, Ganondorf can tournament winner jump from ledge and still have time to get down and land a b-air. Forced jump is super overkill right now.)
? : Idunno, d-smash is good I guess?
60-40 : I played Just a lot before he moved, our games were always close and I believe he is a better player than me. It does seem worse in theory though.
? : Haven't played a good Ivysaur.
50-50 : Call it even because ice beam. Don't really know though.
55-45 : Easy to outrange and camp, he hits like a truck if he gets in though.
45-55: He has much better stage control, missiles aren't that good in neutral because they just hit one of his myriad projectiles. He also gets guaranteed kill moves off of throws.
55-45 to I don't really know: I played iPunchKidz on netplay once. I expected 0 to death combos but all I really got was a bunch of aura sphere charge hitbox cancels into whiffed moves. Maybe Samus is a weird weight for him.
55-45 : I haven't played a good Lucas in 3.5, but I thought she beat him slightly in 3.0.
55-45 : Easy to outrange and edgeguard, but he can edgeguard back pretty well, There are no combos in this matchup.
45-55 : Fireballs beat everything in neutral, cape makes projectile spam more dangerous, Mario gets combos on everyone, Samus included. He can edgeguard her super easily. She outranges him at least.
40-60 : Can't deal with his range, can't get down from juggles, can't survive being off stage. There aren't really any perks to this matchup.
55-45 : Haven't played a good 3.5 Meta Knight, it was probably about even in 3.0 though.
40-60 : Mewtwo outranges and edgeguards Samus pretty easily. Up-throw kills stupid early.
50-50 : GnW can't answer Missiles super well, god help you if he gets in though.
55-45 : Can't deal with Missiles, easy to edgeguard. He gets some ok combos on her though. Grounded d-air leads into up-air to kill at pretty much any percent.
? : I always have trouble if an Olimar comes up on random, probably matchup inexperience, but Olimar is a jerk and he hits too hard.
55-45 : Ice mode makes this so much easier than Melee.
50-50 : Can kinda sorta combo Pika, Samus wins neutral handily. Pika dominates offstage game though, and Samus dies to up-smash->thunder at like 50%
60-40 : This seemed about even in 3.0, people like to say Pit sucks so whatever I'll go with it.
35-65 : Grounded side-b is terrible for her, but it can be played around. N-air kills Samus super early, burst movement is scary. Samus dislikes killing throws. It feels like the worst thing in the world to play this matchup, in theory it doesn't seem as bad. Need to learn this matchup better.
55-45 : Crouch cancel d-smash ruins his life, but Samus still has trouble with swords.
40-60 : Still most of the problems from Melee, crawl helps a little.
50-50 : Easy in neutral, but die to upthrow->c4 at 60%.
55-45 : His up-air kills early, he doesn't have a reliable setup on her anymore though to the best of my knowledge.
45-55 : Armor through or slide under missiles, kills her at like 80% from up-smash or up-b, he can sorta combo her. Charge shot invalidates his existence though.
35-65 : This feels impossible against random Toon Links, definitely need more practice in this. Better zoning, too fast, spooky green boy.
60-40 : As long as you dodge the clap this is pretty easy, missiles and nooches.
50-50 : Wolf dies when he's offstage ideally, Samus can combo spacies pretty well. Wolf wins neutral though, new lasers are very good. He can also combo her, cause he can combo everyone.
50-50 : Not really sure on this one, need to play some good Yoshis. He can't answer missiles all that well, but Yoshi deals too much damage with a few hits, and kills vertically fairly well
40-60 : Nayru's love is just plain annoying, it sucks to be punished for a move that you predict perfectly because the reflect box lasts practically the entire animation, and there are hitboxes that stretch a mile in either direction. And it land cancels, hooray. Also d-tilt leads into up-tilt that kills Samus at like 80%, other random vertical kills that negate her weight. If it weren't for Nayru's this would probably be Samus favor.
45-55 : Hated this matchup in 3.0, haven't really played it in 3.5.
Anyway, all Samus players are bad because it's hard to ever choose the correct option because she has too damn many tools.