Well, Mongoose was originally considered a serious threat to Thor because of his combination of strength (Class 25 or so) and super-speed/agility. This enabled him to whip Thor pretty badly at one time, although he had to soften up Thor with special gas, IIRC.
Later, DeFalco seemingly changed his mind, and had him beaten easily by Thunderstrike (a watered down version of Thor)
The Crusader (a mortal empowered by belief in Christian fundamentalism) butchered Thor at one time, almost fatally skewering him, although the circumstances are a bit open to interpretation. Odin said that Thor doubted himself, which greatly weakens a god. When Thor returned with confidence, he whipped Crusader easily, and embarrassingly.
So it really depends on a lot of factors. Thor is susceptible to nerve strikes, which once allowed Mantis to down him.
She defeated a real Thor with a nerve pinch ... as ridiculous as it is