Smhh 'Ness can't do anything in air (besides bair)' wuh bout retreating fair tbh.
We have Dacus.
Edit: Rather than just contributing little to this, why not give my own thoughts on this MU?
From personal experience, I'd have to say it's at least 60:40 nothing higher. Maybe 65:35 at Least, the highest number being for Falco.
From experience, Ness usually uses Fair, Bair or Pk Fire as an Approach, now, if they're spaced properly, and they retreat on them, we can just shield, or Nair Oos/ Bair Oos to punish, to punish a Fair, I go with Dash Attack Oos, Usmash, Boost Dair( Input Dash, Short Hop Dair), Or a Nair, this Implies they hit our shield. If not, and they approach, Falco can just camp lasers.
Now, we can't really do much with our lasers in this Mu since the have the Psi Magnet, but, we can still force an approach, just fire lasers in the other direction and Iap when they get close, or Bair/ Shield grab them.
Now, if they Pk Fire, you can Ps it easily, if they're close, reflector, this way they get hit, and if they catch you with Pk fire as a punish, smash Di away and down while holding shield, you should be able to roll out of it, on chance, you can reflector it while being hit by it. I only know this from playing Marth, Marth can do the First hit of Dancing Blade to interrupt Ness/ Counter Pk fire entirely, as Falco's Reflector, Dancing Blade(Hit one) and Counter all are active on frame 4. This kind of makes Pk fire unsafe for Ness now.
Now, when I land a Grab at Low damage, I don't usually CG to the ledge, I Dair early so I can get a Read off of them and follow up with an F-Smash/ Dash Attack/ Dacus/ D-Smash/ Jab/ Grab/ Shield Grab. It works.
As for when you're recovering, Phantasm is easy predicted. You either land on stage or go for the ledge. Now, here's a trick around that, if they go near the edge, go for the stage, if they stand about 3/4's of the way on the stage or even 2/3's of the way, go for the edge. Also, i always go for a Long cancel, it gives you a boost so that, if they catch you onstage, their spacing will be off because they weren't expecting you to cancel.
Now, for when Ness is recovering, if he just drifts to the edge, or Jump to it, do one Jab, this will interrupt them and they'll end up under the stage. And if they're far enough to Pk thunder, stay near the edge and instant snap to it before they reach it, if timed properly, They bounce off and die. In other words, Ness should have an Issue recovering.
At high damages, for Ness, I like to Air release them just to scare them, implying I land a grab, if you're at Low Percent, Ness isn't going to approach you often, so, wait for a Punish to Usmash or do a Smash in General. Or make a read with Dacus.
When you're in the 130-140% Area, then Falco, Worry about B-Throw. Before then, if you have good Di, you'll be safe
I'll put more later on, if you want to talk to me, Leave me a Message or, add me on Facebook.
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Also, side note. Every move that's in the Air that has Horizontal or Vertical knock back will stage spike even a few ground moves will.