We'll be using the new and improved Eternal edition manga for Usagi. This is essentially the 'perfect' and final english translation of the original manga.
VS
Round 1: Lambda Usagi vs canon SSB/UI Goku from the DBS Anime and Manga
Round 2: Speed equalized
Round 3: Bloodlusted
Battle takes place at the Galaxy Cauldron or Universe 7
Please note this is not Sailor Cosmos but Usagi using the Lambda Power from the Cosmos Crystal (no known differences power-wise)
that's more of a quirk of how DB's cosmology works than anything Goku can actually do himself
unless the fight takes place within the DB universe I can't see it coming into play?
Also never defines whether it is impossible or not for a mortal to do so compared to a god. It could very well be that divine beings are granted this special permission due to their status.