The Mouse would take on anything. It would have no problem having a crack at the Honey Badger, and if it could swim, I'd imagine it would have a go at the Orca.
Remember, they all frighten elephants. This one would kill an elephant, eat it, and then sell its ivory to some dodgy Triad gangster...
Why does everyone have it in for the mouse? Yes, it's a mouse, but a bear is just a big cuddly bear as well.
This mouse just takes it on the chin with every prey it encounters and still beats them. That's pound for pound hard.