[Blake takes down one of them and a shit ton of smaller grim riding it]
Yang:

since we now know that grimm come in all sizes (as seen with these tree sized mammoths and the miniature nevermores) and can go from mindless to highly intelligent, how about
tiny insect grimm that have lethal poison. they could sneak into homes in the boonies and would require traps to kill.
half grimm: combinations of grimm and normal animals possibly from a parasitic grimm inhabiting an animal body. maybe this will happen to zwei (could we handle that kind of emotional shock)
human grimm or weregrimm grimm that are humanlike in shape and intelligence. they command hordes of lesser grimm. or possibly someone creating something like this. a grimm with aura and control over other grimm creatures.
grimmlings grimm that can disguise themselves as humans. because of their tough hides and strength they can do things that a human with aura can do. could roman be one of these?