Only airdodge if they're close enough to do a strong/kill move and you're reaaaally scared. If they don't do a move, you'll get punished every time. Watch how the good Samuses return to the stage.
I also have a problem where I try to input the same thing multiple times; it's very dangerous, heh. Get used to doing things after stun ends, or at least go for an "option-select" type thing: only repeatedly do inputs if you know it won't get you in a bad position regardless of what they do.
To edgeguard a spacy going for the ledge, you should either ledgehog, missile/chargeshot if they're high, homing missile if you think they'll up-b, dangled ftilt, dangled fsmash, or dsmash. They actually have a lot of recovery mixups--saving doublejump, shine stall, walljumps, different forward-b heights, different up-b angles, etc. Jumping out with a nair won't work unless you catch them in their initial up-b animation or if you stick your foot in the path of their forward-b.
I also have a problem where I try to input the same thing multiple times; it's very dangerous, heh. Get used to doing things after stun ends, or at least go for an "option-select" type thing: only repeatedly do inputs if you know it won't get you in a bad position regardless of what they do.
To edgeguard a spacy going for the ledge, you should either ledgehog, missile/chargeshot if they're high, homing missile if you think they'll up-b, dangled ftilt, dangled fsmash, or dsmash. They actually have a lot of recovery mixups--saving doublejump, shine stall, walljumps, different forward-b heights, different up-b angles, etc. Jumping out with a nair won't work unless you catch them in their initial up-b animation or if you stick your foot in the path of their forward-b.