How to chaingrab marth
From 0 %: Dthrow -> side taunt (Don't try me) -> dolphin slash misses -> regrab -> repeat
No, but really. I can't see the big fuzz about switching out throws against marth. Complete the chaingrab, do some followup, continue dthrowing for bdacus, dacus or just running -> shield grab. All of these works.
Marth is hard, but can be made even-ish, as long as you are good at picking options. Masha makes a great example of how to play against marth, by simply doing the right options when pressured, because that's what you're gonna get against marth: pressured.
Gonna talk about a few pressured situations where you would normally have died, but are going to survive instead. Spoiler: This will not work online.
First it's probably the easiest one. The cg -> spike. Heck, people forget that you can SDI tipper moves like a GOD unless it's fsmash. Personally, my SDI is on and off. Either I get a perfect SDI, or I miss it completely and I get spiked with a bad reacted meteor cancel. I don't know if that's common, but i suggest mashing DSSDI at the ready when he's grabbing you and you know he's gonna spike you. Control stick til the right if you're on the left side, and on the left if you're on the right, and c-stick upwards (if he misses you will not be fairing to your death, but doing an uair that you can survive with).
Then, imagine that you're down there with him in the tough spot. Now here is the tricky part. Your tech skill must be good, but that's what you gotta expect to survive what people call "a guaranteed death". Personally, I use Y as shield due to tight spots like this. Fast power shield, fast techs etc.
You're banning lylat and marth is banning fd, so most likely, this will happen at either BF or SV. You are below the edge with a charging firebird, marth is holding the ledge. You WANT him to hit you against the wall, because when you tech jump, that's your save. But unfortunately, smart marths doesn't fair or up b you... yet. They use side b to interrupt your up b while spacing away as you fall down little by little. To survive this you can do one out of two things. Keep your finger on the shield button and NEVER CHOKE WITH AIR DODGE!
1: Mash up b. Keep a constant eye on marth for whether he's using his up b. Make sure to stand in his way from the up b and to the ledge, because that is your life. What sucks is that he's got another jump, but that shouldn't stop you from being in his path. Once he up b's you, DI up, tech jump and live your life as a free bird
2: This is also very tricky, and is very much about a spacing most marths won't expect at all. This counts as if you tech underneath a ceiling as well. Most people just flare up their wings and marth grabs the ledge with up b, even without hitting falco
what you gotta do though, is spacing to the lowest point you can get underneath the ledge and still being able to reach it with up b. If you have found that point, you have a chance to survive, bro. Space down their as you just teched and your fall speed isn't that great. When you're that far down there is nothing marth dare touching you with, so he will up b back, most likely without hitting you. Your up b WILL hit him if he stays. Most marths will either stay and not believe falco can reach this high (it looks higher when the screen is zoomed in to one tiny spot), or he will try to intercept you last second, and fail. The smart marth will get back onstage before he gets fried by your firebird. Leon on the other hand, will spike on the way up before he dies himself though, so in that case there is no hope.
My pleasure.