I have no idea if it is "mistake rib" or not. It is very easy. The first row of the actual scarf (not including the ruffle) is k3, * bring yarn forward, slip next stitch purl wise*, repeat to last three stitches, k3. The second row is k1, byf, slip next stitch purl wise*, repeat to last stitch, k1.
Repeat these two rows to desired length. How easy is that? As for the ruffle it is just as easy. CO 60 stitches. First row: k2tog across (30 stitches). Second row: k2tog across (15 stitches) then start working on the "Eve ribbing" pattern. Remember to use chunky yarn and size 13 US needles. So quick, so easy, yet looks like I actually know what I am doing and can knit in my sleep. It works up quickly too! I did 13 inches in an hour.
Yes, I love knitting baby clothing and items for children. They are the easiest to please!