Joe, I found your "odd" foot. It's part of a pinking attachment. From a Worthpoint ad:
Vintage Singer Sewing Pinking Assembly Estate sale find. This was all together.. Was used on a Singer 201. Great shape. crinkle finish rare and in great shape.Includes all pieces in photo.Includes Clamp with green felt lining.# on inside of Pinking Body is:121259. # on armature is 121111Pinking blade guard #120994The clamp number is 121316Sealed ball bearing wheel