The Faunus--> Grimm is farfetched according to the show's logic. It dawned on me when I rematched the show. 

Grimm are creatures of darkness, thus have no soul.

Aura is the manifestation of the siul., and is required for both the use of semblence and when using weapons, which are a manifestation of aura.

Blake, a Faunus both possesses a semblence and uses a transforming wrapon.: sure signs of an aura.

Sorry to say, but ERode's theory can't work

Fun police, hooooe