I know there are many mystery quilts on the internet, but I think that if you selected or designed a quilt with two different blocks and a pieced border, you could probably organize a clue/task each month. Do you need 12 months? Most of the mystery quilts that I have participated in were somewhat limited in scope. No one wants to invest the time and money into something they may not even like. You could do something like a medallion quilt with several borders...Just my thoughts