Marth's Ledge Traps and Vice-Versa
Marth on the Ledge
This really isn't a position any Marth wants to be in. Marth is one of the worst characters on the ledge because his options are so limited. Each option he has can be punished. Your opponent doesn't even have to predict you, depending on the character he could just stand there and react to whatever you do.
Notice where Meta Knight is standing. Not too close, and not too far away. Once you are outside the range of your opponent's ledge attack (Marth's is terrible) you have effectively limited their options to very few. Notice what happens if Marth attempts a ledge attack or simple get up:
Meta Knight uses his range to reset the situation. Marth is now back on the ledge with a little more %.
Let's take a look at some other options. Marth can also attempt a roll get up. This has a few invincibility frames, but the real punishing comes when you stand up. Notice how Meta can easily cover this option:
He turns around, grabs you, and throws you back out. You're right back where you started.
Another option.. Marth's double jump nair is often predicted by good opponents and punished:
Snake shields it and throws you back out:
Marth's final option, and one of the most reliable is the simple ledge jump. Of course, depending on what your opponent is doing or how good he is he may be able to effectively cover this as well. Snake can use his up smashes to effectively cover most aerial approaches while you are on the ledge:
Or:
This is a little something I made up. It's simply doing a double jump forward b to stall yourself, hopefully throwing off your opponent's timing. Depending on what your opponent does you could throw out a fair or just land. This is in no way a sure-fire method, it's simply a mix up and isn't that reliable if your opponent predicts it.
These are Marth's basic options, plus a little mix up. I went over this weakness because Marth has no reliable way to get up like some other characters. You have to think when you are on the ledge, if you try to rush yourself and get predictable your opponent will (should) be able to destroy you.
Try some drops > double jumps to just stall yourself there.. get your opponent thinking too. I'd say two of the safest options are ledge jump and regular get up.. I also throw in the occasional roll get up and double jump nair get up. Make up your own strats. Don't be predictable.
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Your Opponent on the Ledge
Alright, now we can focus on the positive! While Marth is terrible on the ledge, he thrives when his opponent is in that situation. Marth is very good at ledge traps. When I look at some of the videos Marths post... You let your opponent get up with relative ease when you should be able to get some easy % in. Let's take a look...
Snake is really bad on the ledge, possibly worse than Marth. If Snake tries a get up attack or a regular get up simply rush him with dancing blade or a grab. You will put him right back in that bad situation.
EDIT: Forgot to mention, dtilt is also a great option to poke at their feet. If it hits their shield they will get pushed back onto the ledge.
A jump get up, especially from Snake or another large character that is easily juggled, is also an easy option for Marth to cover. Marth is great at juggling, especially on Battlefield.
Snake has a rough time getting back on stage, especially from the air. Do all that you can to make it hard for him.
Marth has a multitude of options to deal with a roll get up, dancing blade and grabs being the main ones.
Grabbing is my favorite, all you need to do is turn around and do a dthrow/fthrow (depends where he is going to end up as he rolls, but most of the time it will be behind you). Pivot dancing blade is also a great option.
Some characters are harder to ledge trap than others, Falco being one. What you want to do vs him is be just outside his ledge attack range (obviously, and keep in mind his is rather large), but still be in a position to punish his side b recovery.
Shield or jab the phantasm and punish.
You can also stand inside your opponent's ledge attack range and bait out the attack. This isn't to be abused, but the rewards are great:
I may edit this with more mix ups/trap options later, but these are the basic options for Marth when on and off the ledge. Most experienced Marth's should already know about this, but it's always a great refresher. Don't overlook this, it's important.
Know that some characters are much less susceptible to ledge traps, such as Meta Knight. He just has so many options that he really doesn't need to worry about it.