Okay, I'll use time stamps to point out things and then give an overview of your gameplay.
1:01 - That was a very unsafe up b. You were easily in position to just catch the ledge which would have been the better choice.
1:05 - I'm guessing the up b was because of the clank there so i'll let it slide but just saying that I saw that >_> lol
1:12 - Try to learn the spacing for side b. Marth was clearly too low. After the first hit whiffing you should have stopped there and changed tactics. You do the side b as an edge guard a lot but he's almost always too low. Holding the edge and forcing him onto the stage or doing the light shield thing would be a lot better.
1:14-1:20 - There was just a lot of sloppy movement and spacing here. You should probably return to neutral and dash dance after stuff like that because continuing can be very unsafe. The marth didn't really punish you for it though.
1:32 - Marth landed on the platform so it should have been obvious that an fsmash wouldn't have worked. Wavelanding on the platform and shielding or just an uair would have been better overall
1:35 - You waited in your shield way too long. Seeing that marth was facing you in shield should prompt you to run to avoid a grab. Heck he had enough time to land, shield, and shield grab you while you just sat there in your shield.
1:38 - Since marth was on the ground and hadn't done any moves, any ledge option without invincibility was unsafe here. Rolling or ledge hop air dodge would have been a lot safer.
1:49 - Flare blade is a horrible edge guard against marth. Again holding the ledge and forcing him to get on the stage or doing the light shield thing is much better. You do this a lot throughout the matches and you were punished pretty much every time. This is the only instance I'll point it out though to save me time writing lol
1:54 - lol don't roll so much. Hella unsafe but the marth just didn't punish you for it.
2:00 - Hella unsafe nair. Any full hop aerial is gonna be unsafe if marth is on the ground
2:12 - lol nair the wrong way
2:14 - After the seeing he missed the tech, waiting in shield would have been the best choice to cover all his possible options. From shield you could have shield grabbed the get up attack or wavedash grab to catch any roll.
2:21 - A grab here would have been much better than a dtilt.
2:31 - I looked liked you charged the neutral b a little bit before letting it go. If you are gonna jump out there and do that move make sure to get it out immediately so that your opponent doesn't have time to react with an air dodge.
2:36 - Another bad side b instance
2:50 - Another bad full hop aerial.
2:56 - Why you stand there so long? lol
3:03 - I don't think I need to say what went wrong here lol
3:09 - This is where you'd want to use a neutral b. When marth and other floaty characters are at high percents, that is the only move that you can follow an dtilt with.
3:14 - Try and space side b a bit further back so that you aren't shield grabbed. Kind of a more obvious thing to point out lol
3:22 - That was a counter out of fear. Try not to do those. Try not to do anything because you are scared.
3:30 - Bad side b. Should have grabbed.
4:00 - Don't forget that marth's aerials come out really fast so be careful by the edge. An ftilt would have been a better choice because of it's faster speed.
Well I think I'm only gonna comment on the first match because this is starting to get long and the second match was a lot of the same kinda stuff. The main flaw in your gameplay is your lack of knowledge of roy's threatening range. You apply very little pressure. Roy's grab is one of his key points in doing this and you grabbed very little in the matches. You're punish game is very lacking as well. There were many opportunities where you could have made a counter attack but either didn't see them or had positioning such that you couldn't react to it even if you did see it. Working on how to pressure more with dash dancing and what things you can do from there is what I think should be your first main focus. Also a lot of your follow ups seem like you have an idea in your head and you try to do that regardless of how your opponent DI's. You need to watch your opponents DI and adapt accordingly. Try to have positioning such that you can cover all his options or react to them. I didn't really cover the positioning stuff but I think this gives you a good start on improving your game. I hope this helps.