Marth edgeguarding is tricky.
If you're recovering from below, down tilt does not gimp unless it tips, and I've honestly never been knocked out of my DJ from a tip down tilt before, so I wouldn't know the percentage to break, but it would have to be at least 80%, making an educated guess. It can gimp if you plan to egg to grab the edge, but Marth ALWAYS ducks before doing his down tilt waaaaaaaay ahead of time, so it won't be any big surprise. Forward smash can also hit below the stage just a bit. Forward smash tip stops Yoshi cold at 60%, so if they're at the edge, try to ride up the stage and DJ through the weaker part of the sword. If they're at tip length from the edge, then try to pull back as you reach the edge or you can aim for the walltech, which can be tough (but very possible).
Recovering from high (or recovering when your DJ takes you high above the stage) can also be kinda tricky. Most gay Marths will simply follow the direction of your DJ. If you're recovering from the left and go high and right, they'll simply walk under you, waiting for a chance to forward smash you out. Others will simply try to forward smash or neutral B (which is actually kinda dangerous). You don't have to worry about aerials, even tipped ones, until your damage is just ridiculous, so just focus mainly on avoiding early tippers with forward smash and the B moves.
Dancing Blade edgeguards are rare, but the ending strokes are all very potent, so do watch out. Reverse up tilt is super homo, but nobody does that thankfully.
So two things to conclude this. First, if you DJ through a sword attack that's not a multiple hit attack (like neutral air) and it has suitable lag (forward air, forward smash, NOT DOWN TILT), then cancel your jump after you get hit with a neutral air to create space and to tack on some damage. Trading isn't bad in this matchup. Also, really
really gay Marths will grab you out of your DJ. Watch out for this. It's a very deadly technique, especially down tilt to grab. It *****.
I guess the point here is that you need to find out where they're most comfortable edgeguarding you and trying to abuse the weaknesses of that particular position. Marth doesn't edgeguard too easily in this matchup, but it can seem like you run out of options really quick when, in fact, it's Marth countering your recovery game instead of you countering his edgeguarding game. Stay positive and stay alert, jump through weak sword attacks, do lots of math inside your head so you know when it's safe to attempt certain recoveries, and last, but not least,
don't cancel your jump early for any reason. This last tip should be pretty self-explanatory.
You can bump the thread, if you like. Bringer's a good mod, so I doubt he'll mind. [/speaks-on-Bringer's-behalf]
I'm going to try my hardest to get videos from VLS next month so I have some recent material of my play and I'll try my best to have it against good people so you guys can see for yourself what works and what doesn't. Not all of my stuff works on everyone, it's just how I've learned to play against the people I've played during my travels.