There's actually a fanfic over on SB that I think does Grimm more justice;
"The Games We Play" by Ryuugi is a AU where Jaune gets a different semblance that gives him the powers of the MC from Korean webcomic "The Gamer". In it, he depicts the Grimm as endlessly evolving nightmare-creatures that have successfully destroyed human civilization countless times, yet for their own reasons never actually finished the job. The do also have an ultimate master similar to canon, but he's far more interesting and threatening than Salem could ever be, not to mention far more terrifying in concept.
I mean yeah, it does turn into something of a powerwank fic, and almost none of the main characters from the original show are focused on for any appreciable amount of time, but it's still a fair sight better than anything Rooster Teeth has managed to produce; it even turns Adam and Raven into interesting characters.