This is pretty much impossible to answer. The dimensional superstructure in DC is a LOT different than the dimensional superstructure in Marvel. Afaik, Marvel doesn't really have anything like DC's 6th dimension.
That said, if Mxy couldn't have accessed it under 'normal' circumstances, then it's hard to imagine anyone in Marvel doing so.
I had an argument with Galan before about how mxy power levels would be portrayed in marvel. Mxy would be top 20 at best in the marvel hierarchy. He's destroyed dc one time in a non canon comic and never once replicated that ever, we can disregard that as PIS/outlier, even if that was the case, dozens can also destroy reality in marvel. Its not that impressive
a.) All of Mxy's appearances are canon. This has been explained to you ad nauseam. Stop being willfully ignorant/trolling.
b.) Mxy's feat in WF isn't an outlier. Aside from the fact that the comic itself indicated that Mxy and Bat-Mite destroy/recreate the whole of DC EVERY TUESDAY for the lulz, we also don't see Mxy routinely creation-busting, because destroying existence is boring to him: (please log in to view the image) "I actually grasp the concept that if you obliterate reality, then there's nobody left to play with!"
Who in Marvel has destroyed every single numbered dimension in the company(and keep in mind that higher dimensions scale infinitely above the 3D multiverse in DC), along with the infinite pasts/presents/futures of multiversal Hypertime... Then recreated it all with a snap?
Destroying Marvel's multiverse is literally nothing compared to what Mxy's done.
Based on the fact that DC's Multiverse is NOTHING compared to Marvel's. I wrote a 12 page essay with documented scans etc about how Marvel's cosmology is superior in every aspect, I can gladly share it if you want. Just ask