Doods. When MK ledge camps, run over the ledge and put your shield up. What can he do?
Fair?
Nair?
Shuttle Loop?
Tornado?
The shield will stop all of those. When your shield starts to get tiny, roll away and chill on the stage for a couple seconds and try again. You're even happier if you have some projectile you can pepper the ledge with, but not all characters have that option.
Most metas try to shuttle loop because it's fast and BA. After he loops, almost all characters can jump and use an aerial and metaknight will get hit because unknown to them the shuttle loop puts them in the same vulnerable spot everytime, and you should be punishing it at about that same frequency. Thus, meta is going to shuttle loop a lot less because he gets hit hard for trying such a thing.
Fair and Nair are harder to punish, but most of the time if you can hug well enough or predict it, you won't get killed by anything he does, it's just a matter of being accustomed to invincibility time on the ledge, and knowing how long to wait in order to pressure the meta... without waiting so long that he taps you with something that gets you stage spiked.
Whenever dealing with the tornado, I make it a point to point my shield upwards. It could be purely coincidental and in my head, but it stops it from poking frequently, and if it does poke it, your upward DI will most likely pop you out of the tornado in one hit.
If the meta is silly enough to stay on you for the duration hoping for the shield poke, as soon as it's complete you can point the control stick towards them and tap z and bam, free grab.