Ah ok, I see now that my question from the large discussion is answered here. "Rōvys" does indeed have a different ending if it's in the accusative case.
always think it's plural because ends in "i". /me shakes fist towards old valyria
The more I progress in this course, the more I'm convinced that it's not a very good language because the different declinations are so very different and there's a lot of ambiguity of you don't know the exact gender and class of the word.
It sure feels like there's a lot of complexity simply for the sake of complexity, as if the author tried to add every obscure peculiarity of natural languages he could think of. Of course, it doesn't help that the course is only available 'from English', which means many words or sentences that would have a straightforward translation in lots of languages need a very unwieldy translation in English to be remotely accurate.
Well, it does seem that he wanted to emulate ancient natural language, heavily latin.
If more speakers contribute to more courses in the future, we will indeed have more than the "from English" course. But be prepared for the wait.