Combo him with Shine DJ Dair until.....roughly 42%. Then start pushing him offstage or mixing in Utilt Dair platform tech chase(unless he's by the edge then the tech chase is easy anyway.) If you push him off high it's okay because then you can just Bair him a lot or shoot him a lot or both for free damage.
Edgeguard Marth when he's close by seeing if you can force a swing. If you can then just shield and counterattack or CC. Marth can't do anything off of a sword hit if you are preparing to counter it well. Most Marths grab the edge now so you can just grab the edge and rising Bair him. The idea, as you're kind of seeing, is to kick Marth away until he has to use his DJ and start up-B'ing.
When he has to up-B, there's an interesting game that begins to be played. You, as Falco, can DJ regrab the edge on reaction to Marth's side Bs and otherwise wait through the up-B. Should you mess up or be caught without edge invincibility, you can still DJ backward/in place to regrab the edge OR do an edgestand into Dsmash. DJ'ing backward is for when Marth tries to up-B right to the edge(you will grab it first), and edgestand is for when Marth does up-B far away to avoid an attack or goes into you(probably onstage.)
Recovering vs Marth is just one of those guessing games you go into without caring LOL. You have to pick stupid options sometimes and if you're scared you won't do it. Side B'ing higher into Marth is good for going through his jab, going high then side B canceling is classic but still very good. Try not to up-B to the edge terribly much because Marth's like Dtilt. Going low however is pretty good because it lets you tech to side B him or the edge so that's super powerful. Delay the tech input on counter btw.
Edgeguarding Sheik is just grabbing the edge and sometimes rising Bair lol. Doesn't matter if she gets the edge kinda like Marth you can just do the Mango thing and get on a side platform and drop Bair her. I'd rather shoot into attack/throw during their lag but that's me lol.
Sheik can't cover the edge well at all so going to the edge is great vs her.
I lost 66% of the matches, but every match was last stock, usually last hit. Unless the stage was FD or FoD in which case sometimes it was a blowout in my favor, or DL a blowout for him lol. I consider the losses to be based more on my lack of vs Falco training with Marth than a matchup thing. My Marth could totally handle Falco with more training and I learned a lot playing vs Mango(jab and Ftilt are apparently good in the matchup, for example.)
I always figured that recovering v Marth was impossible if they know what option you want to do. I guess I was right that there is no reliable way to recover against him but to be unpredictable *sigh*
Thanks for the insight, it really helps. Especially the delay on teching counter....didn't even know you could tech counter. MUST TRY
Do you have any advice for comboing Sheik? I never know what to do after connecting with a hit/getting a grab. You always seem to be able to combo her pretty well.
As to your Marth vs Mango, I was only going on hearsay as to what happened. I guess I was incorrect, but I heard that your Marth got destroyed. Obviously an overstatement by Mango fans lol
I still feel like your own Falco would destroy your Marth. Your Falco v Marth game is too good as Falco
Thanks for the continued high quality posts, insight, and advice. Much respect, i look forward to hopefully playing some friendlies with you at Apex!