Mystery sewing foot
 

http://imgur.com/gallery/9QW56jthttp://imgur.com/gallery/9QW56jt
Does anybody here know what this may be used for? I got it with my used Viking 1100.

Its marked with a C. It's obviously an overcast foot, with two pins that hold the bobbin stitches far, far apart. But what is that little nylon brush for?

Is there a picture or link?

I've seen overcast feet both ways- with the brush, and without. The brush is the "imaginary" edge of the fabric. The brush provides a something to stabilize the stitch at the edge when there's no fabric to help lock the stitch. As the stitch is formed, the thread pulls off the brush as the fabric advances.

Here is a youtube video..there are several, I just picked this one randomly

https://www.youtube.com/watch?v=aoOJ6qp6sg8