When is this matchup changing?
Marth: 55-45 Samus's favor (according to a former Marth main that I constantly spar with)
How to win:
Spacing is key here.. Marth has an incredibly fast, effective, safe, aggressive rushdown game. Samus needs to dash away and punish, punish out of shield, and bait predictable, laggy moves like fsmashes. Uncharged shots stun enough for ftilts to keep your space. You basically want to keep marth at ftilt/grab's length away most of the time, until you can get him off the edge. If the Marth gets too close for comfort and tries to do a full swords dance, try to shield. If he's not smart and continues to mindlessly input the combo and poke through shield with a down/green hit for the fourth part of the combo, you can wait and get a free shield grab on him. For breathing room, dtilt and dsmash are good so that you can pop Marth up above you in the air. His dair isn't too great, so if you can juggle him with uairs or get him stuck on platforms above you on stages like Battlefield or Yoshi's island, he'll have a hard time. Then get him off the edge!
Gimping him is really easy because of his limited recovery. If you can't hug the ledge fast enough to tether-gimp, you can do a bomb drop gimp and hope it hits him on his way up. If the Marth is too aggressive and comes after you off stage, dodge until you're pretty far under the stage. If the Marth will follow you, he'll be forced to sooner or later up B back to the ledge. If you can bait this you can lead an uncharged shot to interrupt his up B, or you can tether to hog the ledge.
TLDR Version: space away with ftilts, up B out of shield if he doesn't space fairs, use grabs to get him off the edge, gimp with tether hog, uncharged shot or bomb drops. If you can, get him above you in the air.. Uair juggles him well
Watch out for:
Fair juggles, tippers when you mess up your spacing, grabs when you camp shield too much, swords dance pressure.. Also, I notice it's hard to recover against a Marth if you recover too high. Getting up from the ledge can be hard too, because Marth can up b OOS or shield grab your fair if you don't space it right, he can short hop over any ledgehop zairs and punish you with his quick aerials, and he can walk to space a tipper from most of your ledgehop recoveries. His fair also eats through missiles and such. Dsmash also hurts if your shield is low from camping in it as well. His uair juggles Samus like crazy because her dair is too slow, so make sure a marth is never below you like that. Marth punishes mistakes and lag, and lots of Samus's moves leave her open to them....
