marth is interesting cause mid level players get freaking pwnd by marth badly while higher level players do much much better with the MU the important thing with marth ive found is learn how to get in.
i have a bit of a marth problem but i understand it a bit better after fighting marths all over. your shield is his worst nightmare. Chu can beat the living crap out of marth when it comes to up close and personal fights. marth doesn't like the pressure very much at all he likes setting up a wall. its his comfort zone so IMO your best bet is make him uncomfortable ;P
he pwns the crap out of you when your trying to recover to and you have to hold onto your second jump and be ready to recover at an opening also when hes recovering if hes out of his second jump a T jolt can kill him which i always found hilarious. also our thunder really screws his recovery he can still recover on it but sometimes if you trap him with it hes forced to take the thunder or die.
we also pwn the crap out of him if we our below him i find if im under the platform hes on you have a crap ton of options you can do to him.
one thing about marth to is look at his swings. i find have enough lag between his sword swipe that between your shield and your speed you have the tools to break through his wall. make sure you know some of his gimmicks though like Double fair into Fsmash and IIRC he has grab release on us at 0 that scores a bit of % off the bat like i noticed marth like going for that damage so dont be surprised if they try grabbing you off the start.
if you jab him he can Dolphin slash out of it if you like fishing for trips for kills at high % take note of that. and Fsmash outrages like all of his moves (he can punish it though so dont overuse this) and you want to punish the heck out of his landings This is one thing to remember in this match up if you remember nothing else.
and his Fair is stupid it can block your Jolts
get crafty with your jolts, i like looping them around platforms and throwing them when between his fairs if hes trying to zone you with them. just throwing them out though i dont find works nearly as well if the marth knows he can block your jolts with this move closing space on you. he can also kill you pretty quick if you get tippered learn the range of that.
aside from that i know Esam fought Mr R and Leon within the last year and theres vids floating around.