Grab the ledge. Shine spike him during invincibility if he's below you. If not, JC the shine into a firestall. Repeat until he is about to up-B. Shine bair; if the shine misses, the bair should hit (at low %s you can DJ into shine for more KB). If he up-Bs onto the stage as you are stalling with Firefox shines, just LH a bair to knock him back off. Be ready for ground tech rolls and simply punish with fsmash (you should be close enough that you won't have to move).
Things to keep in mind that you will probably mess up when you try for the first time:
1. REACT to up-B. Don't get scared and roll. When you get good at managing your invincibility, you will rarely have to worry about it anyway. At really low %s, even if he hits you with the non-sweet spot, you can still easily LH out of the super low stun and bair him off.
2. REACT to side-Bs and DJ fair attempts. If you are managing your invincibility right, you should never be threatened by this. Right before he gets in range refresh your invincibility, then shine-bair (shine in case he FFs, bair in case he relied on hitting you or if he up-Bs). If he is too low to hit you with either move and doesn't have a DJ, DO NOT ROLL. REACT. If he side-Bs or DJ fairs you while you are invincible, obviously just shine spike (would still just shine-bair just in case you somehow miss the shine).
If he is recovering too high for any of the above to be guaranteed, guard the ledge without grabbing it. Be close enough that he cannot just fall to the ledge without getting baired. If he side-Bs, REACT with FH bair. Trades easily. Fair is harder to trade with, but only if you react really slow and he gets the low hitbox out. If they are ballsy enough to dair, either get to them with a bair before they get it out in time or shield it and bair OoS. If they air dodge
perfectly, your bair will whiff, so FF to the ground asap before he does. Shine, or if you have time, bair/dsmash to knock him back off. Shine and bair are the best if you can hit him before he lands and regains his jump.
Basic Examples:
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