"mit" is followed by dative in German. In Latin, ablative and dative are very close and which is very close, a lot of forms are indistinguishable.
That doesn't change anything else you said, though :)
That doesn't change anything else you said, though :)
And of course, as everyone has already mentioned, spookie's comment is complete nonsense because the case is required, and fully explained, by the prepositions.