The mistake rib is a very straightforward stitch. It is perfect for scarves because it creates a fabric that is reversible, elastic and also lies flat, unlike a regular 2X2 rib. The rib pattern works well for many different yarns. The pattern is definitive enough it shows well in a soft, fluffy mohair or a chunky slub yarn. It is even suitable for a beginner project.
Here's how to do it:
A multiple of 4 sts, minus 1. For example 15, 19, 23, 27...
Row 1: K1, *P2, K2*. Repeat from * to * to the end of the row.