Son Goku vs Thor, with a twist

[The Drunkard Kid]

Don't forget Gohan. Guy fought Super Buu with Gotenks absorbed, and dominated. That version was almost certainly stronger than the Kid Buu that SSJ3 Goku and SSJ2 Vegeta struggled so badly against.

Super Buu was actually the one who dominated Mystic Gohan after absorbing SSJ3 Gotenks. Gohan dominated Super Buu after he had absorbed Piccolo.

That said, to make things even harder to determine, base Gotenks was able to fly multiple circles around the planet at orbital level so fast that he repeatedly intersected his own energy trail in the time that it took Piccolo to go from the Kami's Lookout to the ground level at the bottom of the tower that Kami's lookout floats above, and in DBZ they don't generally leave light trails except as a relatively short range blurring effect that rapidly fades away. To make this even more impressive, going at full speed is generally shown to *rapidly* drain someone's power even in relatively short distances (see Piccolo vs. 3rd Form Frieza), but base Gotenks wasn't even winded.

Furthermore, Mystic Buu (Super Buu after absorbing Piccolo, Goten, Trunks, and Mystic Gohan) was pretty confident that he could chase Goku to any place in the universe that he teleported to, before Buu himself learned how to teleport, but he never really got the opportunity to show if that was a legitimate assessment of his own speed.

[The Drunkard Kid]

Oh, and also Dragon Ball characters' somewhat nebulous but still fairly decent ability to ignore esoterics through sheer power-level (thus far, divine wishes with enough power to recreate planets/moons, resurrect entire species, and teleport entire races interstellar distances are unable to insta-kill or teleport people cosmically weaker than end of Z Goku) would probably protect him from anything that Mjolnir could whip out without significant charge time. Although, if Thor hits Goku with an antimatter beam like Mjolnir was able to create pretty quickly, it should just cause Goku to lose that much mass due to plain old non-esoteric physics, though ki should be able to deflect that just fine since it isn't physical matter and I'm not sure if that was how MJjolnir's comic-book antimatter was actually portrayed as working in any case.

Non-Bloodlusted, and for fun, Goku's probably gonna at least hold down his speed to Thor's level and this is probably gonna involve Goku biting Thor and Thor giving Goku a purple nurple at least once. And if Goku goes SSJ3, there's a non-zero chance that their hair is gonna get tangled together if it gets to grappling range.

[Rightoya]

Speed is wonky in Dragonball, but it is enough to be too much for Thor, who was even in his classic portrayal far from a speedster, but in character could i see Goku draw the fight out a bit.