The Superior Mjolnir is the weapon wielded by the Superior Thor. It is indestructible. When Thanatos went back in time in an attempt to destroy Mjolnir as it was being forged, he was unable to, as the same ethereal forces that gave the superiors their powers put an aura of invincibility around it, and put it's durability at something somewhere beyond 1-A. It can only be wielded by Thor, or someone who is both approved of by Thor, and worthy. To be worthy you must have a "warrior spirit," you must have never killed, harmed, or robbed anyone out of spite. You must also plan to use it for a worthy purpose. And even if you are worthy, Mjolnir weighs like 250 pounds, so you have to be extremely strong to wield it. Mjolnir has infinite weight to anyone who isn't worthy, but Hulk, in his Superior Mode, was able to lift it, as in that form, he has infinite strength, which evidently counteracts infinite weight, as Hulk lifted it with no effort whatsoever.
Hulk (see above)
Captain America (but only as a reborn Asgardian)
Beta Ray Bill
Mitchel Keiltica (He was worthy)
Random firefighter (evidently both worthy and incredibly strong)