I have been looking over my previous grimm campaigns and noticed that I used a lot of custom made characters (using the gnome template but altering the traits). This led me to think that perhaps the minor characters listed in the back of the book weren't balanced very well. When I did the math, it turns out the average starting amount of points spent on traits for all of the 7 archetypes is about 51 points. For example, the bully starts with:
Cool 2, Pluck 1, Imagination 1, Luck 1, Muscle 4 (total of 27 points spent on core traits)
Hide 1, Seek 2, Scamper 1, Scrap 4, Throw 2 (total of 20 points spent on playground traits)
Book Learning 1, Industrial Arts 3, Juvie 2 (total of 6 points spent on playground traits)
This makes a total of 53 points worth of starting traits. I did this for each of the 7 archetypes and found the average (51 points). Then you add the 8 points that you get to spend when starting at 3rd grade, which gives the average starting 3rd grader a total of 59 points spent. You can then add and subtract 8 points from that number to see what the average number of points will be at each grade. I used this scale to assign new values to the traits of minor characters in the back of the book so that they will scale properly with the level of the kids. After all, a 2nd grade cat should not have 102 points worth of spent traits when an 2nd grade player only gets 51, that's just not fair. If the character or creature you want to use is too weak for the players, weaker than what you would like it to be, then simply increase the grade, spend an addition 8 points among the traits, and voila! A simple scaling system.
So far I have done everything up to Gnomes (they are very tough to balance due the large number of study traits and only being 4th grade). But when I am finished, will post the newly balanced characters on the forums. The additional benefit of having the characters more appropriately statted for their grade is that it allows wiggle room for characterization. For example, the Gnome as it is has 144 points spent on traits (thats just over 13th grade!) and it is only a 4th grader. By lowering the stats significantly (down to around 67 as a 4th grader should have), it enables the narrator to buff certain stats that may be unique to a certain character in your story (a talking cricket, perhaps, with an actual grade in Cool) without making them waaaaay to overpowered.
The only drawback to this that I have discovered would be characters gaining lots of health just so that they can be scaled to the grade of the players. Let's face it, a mouse, no matter what grade it is, should have no more than a few points of health (unless some quirky, Grimm-lands occurrence has happened =P). At that point it is easy enough to gauge for yourself the health value of what you feel the character should have. With health values between 1-12, it keeps things simple enough.