Have any of you thought of the possibility of using inhabitants of the Grimm Lands as player characters? I mean, what if one of your players wants to be a talking mouse, or something like that. Any idea as to how you could make this work? I know it's not the basis of the game, but it's just a random thought I had.

This is actually a really cool idea. You could do a lot with it. Although, yes, it does kind of break away from the point of grimm, but there are tons of story aspects that can go along with it. Perhaps one of your players enters the grimm lands as said talking mouse and now the kids have to find a way to cure him. Or that could even be the goal of the saga all together, getting their normal selves back. It'd be a cool twist to have the bully become a mouse, the nerd become a bear, the dreamer become a pidgeon, outcast becomes a butterfly, the jock a sloth, the normal kid...unaffected perhaps a platipus...something not normal, the popular kid a cockroach. Basically the opposites of all their stereotypes. Or a kid has a choice to give up his human form and become some other character - a marionette, be cursed and turned into a gnome/dwarf/goblin/anything. I don't know about everyone else but I will be obsessing over this idea haha.

Like LM says, it is certainly a viable idea, but it does kind of alter the environment. The way I read it, the Grimm inhabitants, with the exception of the major NPCs, are pretty two-dimensional - meaning they really have very little individual thought. They are kind of stuck playing through their stories. So unless your talking mouse is a major character from a fairy tale, I would not recommend it.

On the other hand, you could decide that all of the inhabitants of YOUR Grimm realm are thinking, fully realized beings - but then I think you really aren;t playing Grimm anymore. You aren't playing an RPG where kids from our world encounter beings from a land of imagination and horror, but rather an RPG where creatures from a land of imagination and horror encounter kids from our world. No reason you can't do that. it's just a distinction.