Yeah, that one is really hard.
Not that I want to deny Hax his credit for mastering this technique, but first, Magus420 has shown this ledgestall in his auto sweetspot video many years ago, and second, “haxdash” is a somewhat misleading term in comparison.
No, it works like that: You’re invincible from frame 1-30 and frame 31 you can grab the ledge again. This is already obsolete though: I just found out that it isn’t actually the invincibility that prevents regrabbing the ledge, it’s actually an independent countdown that starts as soon as you drop from the ledge and ends after 29 airborne frames have passed. This implies (and all my tests strongly concur) that you have
zero leniency on letting go of the ledge if you aim for complete invincibility. Thus, it is very important to have this one input down to the frame. Everything else – rejump, waveland, fastfall – has a total of 7 leniency frames and is thus pretty easy, relatively speaking, but dropping from the ledge is harsh. Luckily, there are tricks that can help you get this down to the frame. I wrote it in a Marth guide, but it applies just the same for Falcon:
Yes, although invincible ledgedashstall iterations are always 37 frames, so “slow” doesn’t describe it properly in my opinion.
I did the waveland as late as possible with 315° (everything else is impractical on a non-carved out controller and I don’t think other angles would gain an advantage here) while keeping everything else perfect. I personally call it a “late” ledgedashstall.
Also, here are the same gifs that were in my previous post, but slowed down to 1/4 speed:
tl;dr: Let go of the ledge one frame later than possible and you lose continuous invincibility.
Edit: What the hell. Did you guys know Falcon has another, way simpler ledgestall? I feel like an idiot, probably everybody knows about this because Magus420 elaborated on it 7 years ago. Still, I’ve never heard of it, so I felt like sharing it here: