Limit Climhazzard OOS will become big in the meta, in my opinion. Characters that can kill out with an OoS option have always had a nice little niche; Cloud has awesome ground mobility and foxtrots so him getting under your spacing aerial with a shield is definitely a thing that happens.
Another great setup, though I wouldn't say it is underused right now like the above, is last few frames back hit of nair -> Running LCS. Kills at the ledge, true combo AFAIK.
Megaman has some cool ones. We all know about MB -> shoryu, which is actually a confirm. The rest I am going to list, unfortunately, are not true confirms and are more things that are safe to fish for and can kill if things go well.
Z-drop MB stage spike -> immediate followup. This is nice, because while you are falling down towards them 1) you are unpredictable, due to MM's great weaving and tremendous fastfall speed and 2) you have some good options to be unpredictable with! My favorites are FF -> jump -> dair, trying to bait an airdodge from the FF making them think you are coming in with a bair or nair. FF -> bair is nice, with good control you can drag them towards the stage for a hopeful nontechable, away to mix up the timing a little, AND you can mix up when you start the bair, which mixes up when the bair will hit, which means you are mixing up how long they are in a multihit. I haven't done the frame-math, but I'm pretty sure no one is reacting - even auditorally- to a f4 bair's start vs when it hits them.
Continuing with the FF options. Nair is also a nice one, the nair hitbox has some great coverage, and since you can keep firing you can even bounce them around down there for some trouble. Really good timing with your FF and jump means you can cover more time via 2 shots, and if you drop low enough to be near them at the apex of your 2nd Jump, you can hit them with a pellet -> nair combo, holding them in place and again making teching kinda hard. This doesn't work out timing wise with the FF stuff, but its more for mixup with a regular bair edgeguard... which, tbh, makes up a ton of my kill pressure because it is simple and strong, and can net you a kill pretty damn early, and comes down to a relatively simple series of chases/reads/option coverage (MU dependent)
The nice thing about these mixups, is that MM's trump is actually deadly. Trump -> bair pretty much has to combo, I haven't tested it but since some do and his is tied for fastest bair... yea.
You can also zdrop at the ledge-standup range, which is for post-ledge mixups. Drop it from high enough with an immediate fastfall, you give them a very slim window to choose a proper getup option, since trump = death and standing up into the blade can combo into at least a nair, but I prefer to try for uair for the damage or just pass through them and bair for the kill/offstage stuff. Uair at the ledge is pretty cool, and covers stuff especially well vs tall characters. I believe you have a frame advantage vs tall characters if they get their shield up.
For characters with bad recoveries, the blade itself can be a death sentence. You can also try for footstools after the hit, to make sure they die if they are at low percentages.
Question: Can you insta-footstool a techjump? That would give me some more mixup ideas.
I just posted these as they came to me, so its kinda disjointed, probably has some typos, etc. I like talking about MM's kill options, since he struggles a little in that department, but you do get some amazing moments with the robot due to your lack of a BnB Kill Confirm where everything stems from. Scatt's double dair vs Hyuga comes to mind!
Closing thought: Seeing how well Zero hits people offstage with fair/bair, with a character with way worse air mobility, way worse jump-variability, a worse projectile for trapping offstage (its better onstage, duh. I wish MB sat there with a little hitbox, but I can see how certain characters would immediately be 99:1 with MM), and a slower bair with shorter range... it makes me think it should really be possible with MM, and with proper play I can never let Thor's Cloud live to 210% in bracket ever again >_<