GG7 and I play the matchup wayyyy differently. He plays it more textbook with nairs and ddcamping. I do risky *** gimps and unorthodox spacing.
I always attack Marth when he's recovering. Uair and bair is the best. If they're smart enough to fair you when you try anything, jump over them and stomp. When they recover low I turn around and knee and just the soft hit will bounce them offstage. If they don't tech they die or you can just grab the edge and wait for them to upB and ****. Even at low percents when they try to grab the edge when you hit them off, jump off and knee where they'll grab the edge (this takes experience to know when you'll actually hit them. Even top players don't know it very well. If you know you won't hit them then you'll get gimped. If you do know you'll hit it's pretty much always worth it).
Uthrow is my fav in this matchup. Let them tech onto platforms and full jump stomp techchase is safe and easy to followup if you miss. At the edge upthrow-uair-knee will **** their survival DI, if they DI far away just follow them out there and uair or turn around at the edge and try to bair them out of their forwardB. If they're waiting to attack you offstage then just pressure them by staying close and then grab the edge. They can't really do anything at that point but upB and you should know how to **** them from that.
Stomp reverse knee duh. I've seen Darkrain do a nair that knocks them back off stage but I'm not sure when that's ever the best choice. I stick with reverse knee, stomp knee, or grab to ****.
Stomp outspaces Marth I think. It's real hard for Marth to uair you out of your stomp. The best thing he can do for you is wait until you land and grab. In that case, bair as you land or run away until you reach equal fighting ground. Get Marth to mistime his utilt and you can punish with a stomp. If you're good at edgecancelling (I am), do that with stomps to bait him and then bair/uair and follow up easy. You really should learn edgecancelling stomps though, they scare Marth from camping under platforms.
Edgecancel bair at the edge is so good too. It really messes up their upB timing.
Based on looking back at my repetitive explanation, I think the most important part of this matchup is pressuring Marth offstage and getting him off at low percents. Other Falcons typically chip damage and DDcamp into uthrow knee, do whatever comes naturally to you I guess.