How do you feel MK does against Cloud? Do you feel he struggles in the neutral? And can Cloud escape the elevator combo?
Oh, I think I can help you. Let's go.
I think this MU is harder at the metagame-level/very-high, but not reaches: bad/horrible MU.
What I have as experience about it is that UAir strings are strong here, but it will be hard to kill because of Cloud weight.
If Cloud have Limit, it will be even harder because of the fall speed increase. So.. if you're not gonna get the kill with the Up+B, reset. (Mach Tornado is a great option if you think they're gonna airdodge, catches Cloud perfectly because of his size)
DTilt from the ledge and Nair are very strong as edgeguard, but if you can practice it a lot, I will bet that Dair is godlike (only active for one frame, so this requires practice).
If Cloud have a Limit charged just don't dash attack around since you can die because his high run speed+Limit moves.
Pivot grab is a great option against L.Charged Cloud if the opponent is afraid of the dash attack/d.grab, but if you will die from a L.Cross Slash in the run, just run+shield or jump around.
If you're in a stage with plataforms, tries to space yourself below them, because full hop Dair is quite a bore.
If you run to much for Cloud, he can start to Dair, I think I punished this with run+shield => turnaround S.Loop.
And most important:
Accept your rule as a baiter.
I don't think we should create a lot of pression and attack randomly at the neutral in this MU because he is a better punisher then we are and since I (at least personally) don't kill him very soon if a don't get a edgeguard, I die with stupid %'s because of rage + MK weight.
Run around with you shield. Provoke with dash backwards -> instant dash forwards, tries some d.attacks and grabs when you're in low percents. When you think you got a opening, try your best to throw Cloud away and go for a edgeguard. Jump to force him to recover low and land to dat DTilt, DSmash(frame 4 if buffered).
EDIT: Another kill option is DTilt ->S.Loop or D.Cape. Since he raises his falling speed with limit, is easier to put them into this setup around 105~115% with Limit (if you want to play this MU often, I would recommend check this percents right) and is very hard to tech. Usually they don't tech this.
-----------Against players who are not that good with Cloud ---------------------------
I said this is harder in high-level play because usually pockets Cloud's are too confident.
They DTilt into shield (you can punish this with USmash OoS, S.Loop, grab, d.attack sometimes).
They fast fall Uair into Shield (UTilt ->Ladder combo, Utilt-> Nair, just UTilt this option).
They airdodge with fear most of the time (what give us a pretty Bair, following Nair, or Dair)
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I think it's a playable MU, maybe 40:60~45:55 at high-level play, nothing absurd.
I'm dividing the cast between my 3 characters so I decided to go Sheik against Cloud instead of MK, but I have a lot of experience on this, and is not very bad.