Friendly 1: You've got pretty bad DI on Marth's throws. Typically, I like to mix up between down-and-out, and up-and-out. It helps make it more difficult for the Marth to carry you as far with fairs. Also, you had a good exchange where you dropped a bomb and it led to a dsmash to dair to fsmash on your second stock. It was an excellent string, but you over committed to a nair that left you no safe options back to the stage, and Marth still had his double jump. It's bad to challenge like that, especially when it covers such few options.
The missile game needs to be tighter. Don't look at missiles as a means of hitting Marth. They're primarily a zoning tool. Try to get your missiles really low, because Marth's jab can get stuck in endlag after cutting a missile, and more often than not, you're going to force the Marth to jump for an approach. This match up is a battle between two ground-based characters, so whoever stays grounded the most typically has a better time. You can notice this in your constant over-extentions offstage that lead to a ledge hog to tipper dair on you for free. The stage is the key, maintain your stage control.
If you've ever watched a smart Marth ditto on like Dreamland or something, you'll notice that a huge part of the neutral game in the ditto is going for d-tilt pokes. It's a similar idea for Marth vs Samus. D-tilts are devastating, so be sure to angle your shield downwards if you're ever shielding to avoid the poke. It's kind of similar for Samus, but where Marth d-tilts, we like to f-tilt. F-tilt is godlike, it clanks with f-smash, and it's just a super good move for maintaining strong spacing outside of Marth's grab range (unless he grabs your foot during the f-tilt, but it doesn't happen often). Speaking of F-tilt, it's one of your best edge guarding options against Marth. A lot of people over estimate the hitbox of Marth's Dolphin Slash, but it's essentially a straight vertical hitbox, and it doesn't last long. Learn your spacing for a down angled f-tilt to sweep your foot just under the ledge, and then learn the timing for missing the sword but kicking Marth in the face. It's not too much knock-back, and can often be surprising to the Marth, so they rarely can DI up far enough to try for the ledge again. You can usually just hold ledge at that point, if they do go for an attempt.
You do something that I catch myself still doing. You worry about getting your charge shot ready while your opponent is off stage. If you know for a fact that they can't make it back, then you're fine. But worry about the edge guard first. You charged up, and then had to roll back to avoid getting hit by Dolphin Slash, letting Marth get to the ledge and, consequently, back to the stage. You can charge up after they die, you've got time. Taking a stock is more important, anyway.
Friendly 2: Dash attacking in the neutral is a no-no. That'll get you shield grabbed by a good Marth, and even if they don't grab you, they can still punish it. The same goes for grabbing, ESPECIALLY standing grabs. Samus dash grabs, because it's pretty much always the better option. But still, don't go for raw grabs. If you're tech chasing, then it's fine, but if both characters have all options available to them, it's pretty much your worst choice other than an empty full hop.
There were a few instances where you went up to punish Marth for being above you, which is good. Unfortunately, most of the time you decided to try for a nair to push him away from the stage. Nair is a pretty horizontal hitbox, it does a poor job of covering above and below Samus. And, it's not disjointed, so you lose to a sword every time. Up Air is your best option when chasing an opponent above you. It has disjoint and can set up for a fair which can rack up big damage, or if you're in ice mode, can set up a kill or an edge guard.
You're really keen on going out there to finish off Marth. Stop doing it. At around 22:45, you just run off to follow Marth down, and end up over committing and needing to Screw Attack to get back, effectively allowing Marth to make it back more easily. Just grab the damn ledge. It's not rocket science, but sometimes it can slip our minds. Grab. The. Ledge. That's all it takes a lot of times.
In both games, you burned your double jump a lot for seemingly no reason. This is one of the worst habits to have, as it's pretty difficult to get rid of. Especially for Samus mains, who traditionally are better off than most other characters off stage, even when they don't have a double jump. Burning your double jump means there's far less you can do to avoid your opponent while you're airborne. And, when you're airborne as Samus, it typically means you lost the neutral. Hold on to your jumps for dear life, and start searching for the right times to use it (avoiding a kill move, juking an opponent out when they try to over commit to an edge guard *hint hint*, etc). It takes a lot of mental practice, and you'll make bad decisions about using it for a while, until you get the proper experience to recognize when you need to jump and when you don't.
Last thing I'm gonna touch on is crouch canceling. It's godlike, right? In certain circumstances, yes. You got caught CCing at inopportune times, like while in range for tipper fsmash, which means you're just DIing down and still going off stage. You also got caught CCing near the ledge, which is pretty much the same result. Instead of stubbornly sitting in one place just challenging Marth to do something (bad idea, because he'll do something, and it'll usually work), you should focus on your movement game a lot more. Get familiar with perfect wavelanding, and dash dancing, and wave dancing, and just really try to make your movement game extremely smooth and fluid. Smash is a game focused around stage control and movement, and this is actually one of the best MUs in the game that demonstrates that notion perfectly, which is why it's one of my favorite MUs to play.
