I approve of Mal's take on the Hammer. Though, I lean towards requiring Inhuman Strength or a minimum Lift to use it (as a must). It is constantly stated using it requires immense strength. One could also give it a Seeming ability that lets it change shape into any size of hammer (including a necklace with a hammer on it), though that adds one to the refresh cost, of course (well, more precisely it makes the refund a -1 instead of -2) as someone already said.
I think technically the iron gauntlets were required to properly wield Mjöllnir, though that might depend on what myth one is paying attention to. There's a fair amount of wiggle room in the myths and you can certainly decide some parts are true and others aren't.
Though, to be honest, I think of all the Aesir, Thor losing his way makes the least sense. He seems even less likely to lose his way than Odin; heck, he's still often referenced in places with Nordic culture and even elsewhere (Marvel comics are essentially modern myths featuring him). In fact, he was and is a more popular figure than Odin. Of course, one can handle this sort of thing anyway one wants.
