No.315
"Breach." That's the name of the last episode.
So, we know Monty takes ques from shounen manga right? Bleach likely chief among them?
okay, well the main baddies for the first few volumes are human spirits that weren't sent on to the next world fast enough.
They're chained to something at first, but eventually the chain shrinks and tears out a hole in their chest, making them go "Hollow."
And when that happens they shift from humanoid spirit into a monstrous ethereal form with a unique mask.
Now look at Rwby's baddies.
All monstrous of some sort, all wearing a bone-shaped rune-inscribed mask.
Now let's take this a step further.
Later on in the series, the MC and crew learn that they can surpass the usual power levels by mixing their usual powers (those of the shinigami, death spirits) by finding little cheats to partially go hollow and add to their own power. The ones that do this are called Vizards.
White-fang wears monstrous masks for intimidation, but I think there might be something genuine there, and the way that probably-yang's-mom-racer-x lady appeared, how Neo reacted to her, and how she carted that mask around all make me wonder if she's found some way to go Partially Grim.
Additionally, there are Hollows that figure they can use the Shinigami tactics, turning themselves partly Back toward their human roots and appearances, but keeping the gaping hole in their chest; Arancars.
Not knowing what exactly Cinder is, but remembering the flavor text and exposition in episode 1, I'm betting that even if she's Not a Grim+, Oobleck's comment that the Really old Really Powerful Grimm get smart, wise up, and have long memories and lifespans is going to imply that eventually they reach human-like sentience.
No.319
Sauce on the pic?
No.341