Superpowered Beatdowns

But if Thor manages to knock down Superman even once and place Mjolnir on him... What could Superman do against that?

^You gotta point. If he can't move the hammer he could pin him down and stomp him half to death.

It doesn't work like that.

You can't place the hammer on someone and have it weigh them down.

Also, there is a counter move, if you grab Thor's hand while he's holding the hammer, you bypass the "worthy restriction" and can throw the hammer without touching it.

It really depends on how much damage the hammer inflicts and if it's above Superman's damage threshold.
Regardless, unless Superman has a solid grip on an unmovable object (considering the power of Mjolnir, it'd have to be really immovable!), Thor would still knock him back/up a great distance.

And didn't Superman lift the tectonic plates in a comic anyway? If Supes gets a hand on Thor, he's doomed.

Edit: I think that was someon else who wasn't Thor but Supes did defintley lift the pyramids of Giza. That alone is six million tons.

Isn't Thor's hammer magic? Supes has always been vulnerable to magic.

I think it is, that's why I think you have to be worthy to pick it up. Maybe, I haven't watched the movie in a while. Buckmana is a genius when it comes to the comics, he'll be able to give you the most accurate and true answer..

Yeah, Superman's toast.

I just checked the list of Mjolnir's powers and well, even Superman can't withstand what it would do to him.
Given that these powers are based on magic and given Superman's inherent vulnerability to said magic, he'd lose and lose badly.

Also, Superman has an inherent weakness that can be exploited.
He's dependent on the light of the sun to keep at peak power levels.
All Thor would have to do is grab Superman, throw his hammer into space and then take him somewhere where the light of the sun can't reach him.

And since Thor doesn't depend on external power sources to remain at peak power, he would have the advantage.

So in the final analysis, even without exploiting that weakness, Thor has the advantage.
Superman loses.

Are we allowed to have kaiju (any kaiju, not just the ones from Pacific Rim) fight another character?

I have a suggestion for a battle in mind.

You know, this turned out in a battle of Superman vs Mjolnir.