Ok, I'll start with the good. You are definitely competent technical wise with marth, but as you've said you main fox, so marth shouldnt be a problem. You're general play and mindgames is pretty solid too. There are a few things I can see wrong with your marth though.
Spacing is the biggest problem I see. Obviously marth is all about spacing, and that only comes with experience. Considering you've only been playing him since summer, I'd say you're well on your way to getting good with marth. There are times when I see you Dtilt repeatedly, (most noticably vs Peach 1) and it doesnt knock the other person away far enough for you to safely follow up with another Dtilt, but you do anyway. Most of the time you got off easy, but in the first game, peach should've CC dsmashed you. In general, you need to work on getting your tips with the sword, but as i've said before, its just experience.
Grabbing is another problem I see. You don't grab enough imo. Marth has a huge grab, abuse it. vs peach, you should be chaingrabbing with F throw at 0-10%. Peach doesnt tumble so you can just run forward and grab again, tech chasing between 10-50%. peach actually hits the floor between these % but you can still chain grab if they DI wrong. at 50-75% you can forward throw, wavedash tipper. Vs fox, obviously you can chaingrab, theres loads of threads on this so just do a little research, but generally up throws to uptilts/shffl uairs to tippers.
Edgeguarding is ok, but its got a lot of room for improvement. I noticed in your game vs fox, fox went really low to avoid getting gimped, and you followed him all the way down and got hit by firefox. You should follow him and when you realise hes going low, jump back up and forward b to edgehog. I notice you take alot from M2K's style (hey we all do it, myself included) but I would reccomend watching other marths too for edgeguarding as M2K knows alot of options he has, so he selects which one he needs and you dont learn the other variations. definitely watch ken, azen, tani etc. they all have good edgeguarding.
Those are the major points, there are a few minor points too. Sweetspotting is difficult but essential with marth. Ive seen many a time where you up B onto the stage (unforced) and get punished (or even worse, you dont get punished). Sweetspotting is a must.
Use ledgehop bair or jump of stage and fair/bair. especially against sheik. It *****. again, M2K does it alot so watch his vids.
Finally, ken combo. Its awesome.
Overall your marth is good, has a lot of potential, and I must admit, its actually very creepy similar to mine... very creepy. Maybe because I use M2K stuff alot too