Spiderwick Chronicles

You have to kill 25 cockroaches for this achievement. This can only be done as Thimbletack. I found this link to a walkthrough of the spots where the cockroaches can be found.
Credit goes to Scotian Bred for making this list.
http://www.xbox360achievements.org/forum/showthread.php?t=57...

During the levels which you play as Thimbletack you'll see a number of cockroaches scurrying around, for this achievement you need to kill 25 of them, given that there are a total of 50, this is relatively easy and you'd be able to just pick 25 off as you ran through the levels, however as there's also an achievement for killing all 50 of them you'll be better off following a guide to ensure you don't accidentally miss one.

I've linked in a video guide because in my experience it's always easier to follow a video then it is to follow a list.

*^{Credit to keungz for the videos}